<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:63488aa8-c8bb-42d5-b1c2-8676cf14c101,g:867e8cca-ff4e-4056-9d61-ab1fb7e344f8-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.quanterix.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="qtrx-20250630.xsd#CONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_b417caf7-e7c1-497f-b9fc-755d014cc423" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_StatementTable_b417caf7-e7c1-497f-b9fc-755d014cc423" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_85663fb5-5981-4746-92db-4930d7313c03" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b417caf7-e7c1-497f-b9fc-755d014cc423" xlink:to="loc_srt_ProductOrServiceAxis_85663fb5-5981-4746-92db-4930d7313c03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_85663fb5-5981-4746-92db-4930d7313c03_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_85663fb5-5981-4746-92db-4930d7313c03" xlink:to="loc_srt_ProductsAndServicesDomain_85663fb5-5981-4746-92db-4930d7313c03_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_fcbc270e-0e9c-41a0-805c-a2757dc1fc13" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_85663fb5-5981-4746-92db-4930d7313c03" xlink:to="loc_srt_ProductsAndServicesDomain_fcbc270e-0e9c-41a0-805c-a2757dc1fc13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_dad9e1c8-aa9b-4b68-a098-25fc9d78df9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fcbc270e-0e9c-41a0-805c-a2757dc1fc13" xlink:to="loc_us-gaap_ProductMember_dad9e1c8-aa9b-4b68-a098-25fc9d78df9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceAndOtherRevenueMember_fbd8554f-e3c6-45b0-8641-c75dc92b76d3" xlink:href="qtrx-20250630.xsd#qtrx_ServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fcbc270e-0e9c-41a0-805c-a2757dc1fc13" xlink:to="loc_qtrx_ServiceAndOtherRevenueMember_fbd8554f-e3c6-45b0-8641-c75dc92b76d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseAndServiceMember_eeea27c1-c3e0-47ab-a5c5-4f1866fcf234" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicenseAndServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fcbc270e-0e9c-41a0-805c-a2757dc1fc13" xlink:to="loc_us-gaap_LicenseAndServiceMember_eeea27c1-c3e0-47ab-a5c5-4f1866fcf234" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantMember_1a0af8a6-0326-4f4c-a5a9-a763df93914a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fcbc270e-0e9c-41a0-805c-a2757dc1fc13" xlink:to="loc_us-gaap_GrantMember_1a0af8a6-0326-4f4c-a5a9-a763df93914a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_651ea96f-be7f-45e1-8a53-8cfb4235cfd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_RevenuesAbstract_651ea96f-be7f-45e1-8a53-8cfb4235cfd3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_498a92a0-5839-4e92-aef9-6e588b242fe7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_651ea96f-be7f-45e1-8a53-8cfb4235cfd3" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_498a92a0-5839-4e92-aef9-6e588b242fe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_4fb67006-7494-4da0-9ef0-9880faae5035" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSoldAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_4fb67006-7494-4da0-9ef0-9880faae5035" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_df151997-e74b-41a2-8ea7-86d5d79fb931" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_4fb67006-7494-4da0-9ef0-9880faae5035" xlink:to="loc_us-gaap_CostOfRevenue_df151997-e74b-41a2-8ea7-86d5d79fb931" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_3056eb87-52bd-4c52-a692-91fcab7327ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_GrossProfit_3056eb87-52bd-4c52-a692-91fcab7327ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_c5ab75e2-9064-4c9d-b2e8-5bf11b454ffe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_c5ab75e2-9064-4c9d-b2e8-5bf11b454ffe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_615f700e-fa04-47e6-81ea-aa705aa5263a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_615f700e-fa04-47e6-81ea-aa705aa5263a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OtherLeaseCosts_7f3cd5f6-e048-4df9-9105-7679b41e3200" xlink:href="qtrx-20250630.xsd#qtrx_OtherLeaseCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:to="loc_qtrx_OtherLeaseCosts_7f3cd5f6-e048-4df9-9105-7679b41e3200" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_3ce259e1-32e2-41d3-bc81-82809f18905b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_3ce259e1-32e2-41d3-bc81-82809f18905b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_77348978-a4bd-4df7-b573-8217ece9a8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a5360e09-3be2-4932-a5aa-d12fd13a6bd6" xlink:to="loc_us-gaap_OperatingExpenses_77348978-a4bd-4df7-b573-8217ece9a8ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_716d5537-a021-4db3-86ab-dd91658270bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_OperatingIncomeLoss_716d5537-a021-4db3-86ab-dd91658270bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncomeAndExpensesAbstract_67643b5c-3d54-446f-90e7-86a0b8597e0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIncomeAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_OtherIncomeAndExpensesAbstract_67643b5c-3d54-446f-90e7-86a0b8597e0a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_8ba6ba39-bcee-4b5d-9f25-009f6691c8a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_67643b5c-3d54-446f-90e7-86a0b8597e0a" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_8ba6ba39-bcee-4b5d-9f25-009f6691c8a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_22fe3bdb-bc78-4d11-8f1f-fd4d21401daf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_67643b5c-3d54-446f-90e7-86a0b8597e0a" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_22fe3bdb-bc78-4d11-8f1f-fd4d21401daf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_e2773d25-120f-41e3-b1c2-a17d48f97c54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_67643b5c-3d54-446f-90e7-86a0b8597e0a" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_e2773d25-120f-41e3-b1c2-a17d48f97c54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_9eb73691-e76a-4b47-8953-e153b8eaf484" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_67643b5c-3d54-446f-90e7-86a0b8597e0a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_9eb73691-e76a-4b47-8953-e153b8eaf484" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_1022f2bc-d10a-42b1-8466-6dcd71f20982" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_1022f2bc-d10a-42b1-8466-6dcd71f20982" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_fb5d8357-c35b-4d58-8e3d-b333da18015e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_NetIncomeLoss_fb5d8357-c35b-4d58-8e3d-b333da18015e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_4741d9bb-271e-4b80-98f1-86dae6857dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_EarningsPerShareBasic_4741d9bb-271e-4b80-98f1-86dae6857dc4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_78bac9df-2335-48b8-aa6c-b09b2c5dda68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_EarningsPerShareDiluted_78bac9df-2335-48b8-aa6c-b09b2c5dda68" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b14f3ac8-aff1-41bc-b52d-a41d21691ed1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b14f3ac8-aff1-41bc-b52d-a41d21691ed1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_75d9f8d7-b931-4288-8f7b-2eefd33d7c95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15e946db-38fc-4567-b504-b9b6544cbb85" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_75d9f8d7-b931-4288-8f7b-2eefd33d7c95" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsScheduleofFairValueoftheAggregateConsiderationPaidorPayableDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#AcquisitionsScheduleofFairValueoftheAggregateConsiderationPaidorPayableDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/AcquisitionsScheduleofFairValueoftheAggregateConsiderationPaidorPayableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_87daeb52-fe16-49e3-9dd9-1268f93f6541" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_915fbd80-732d-48e2-a40c-b9a1bcd234cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_87daeb52-fe16-49e3-9dd9-1268f93f6541" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_915fbd80-732d-48e2-a40c-b9a1bcd234cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_3ddec70e-7cd2-490c-9bc7-8d9d926e624e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_915fbd80-732d-48e2-a40c-b9a1bcd234cf" xlink:to="loc_us-gaap_AssetAcquisitionAxis_3ddec70e-7cd2-490c-9bc7-8d9d926e624e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_3ddec70e-7cd2-490c-9bc7-8d9d926e624e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_3ddec70e-7cd2-490c-9bc7-8d9d926e624e" xlink:to="loc_us-gaap_AssetAcquisitionDomain_3ddec70e-7cd2-490c-9bc7-8d9d926e624e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_f68582e9-d9b5-4acc-bc70-c4c6420d00ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_3ddec70e-7cd2-490c-9bc7-8d9d926e624e" xlink:to="loc_us-gaap_AssetAcquisitionDomain_f68582e9-d9b5-4acc-bc70-c4c6420d00ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_c4390ce0-ce9d-4344-baf9-9099bef91b71" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_f68582e9-d9b5-4acc-bc70-c4c6420d00ef" xlink:to="loc_qtrx_EmissionInc.Member_c4390ce0-ce9d-4344-baf9-9099bef91b71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_4856e96d-24bd-42f1-96b2-a7bc8cf254ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_915fbd80-732d-48e2-a40c-b9a1bcd234cf" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_4856e96d-24bd-42f1-96b2-a7bc8cf254ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4856e96d-24bd-42f1-96b2-a7bc8cf254ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_4856e96d-24bd-42f1-96b2-a7bc8cf254ad" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4856e96d-24bd-42f1-96b2-a7bc8cf254ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8fb41491-61cc-4ee7-b5dd-f2c36f2ed712" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_4856e96d-24bd-42f1-96b2-a7bc8cf254ad" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8fb41491-61cc-4ee7-b5dd-f2c36f2ed712" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_4b2d13d4-a1f0-4118-86e6-62b9f1f26149" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8fb41491-61cc-4ee7-b5dd-f2c36f2ed712" xlink:to="loc_qtrx_EmissionInc.Member_4b2d13d4-a1f0-4118-86e6-62b9f1f26149" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_37aaf15c-f53e-4690-b461-148418e15598" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_87daeb52-fe16-49e3-9dd9-1268f93f6541" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_37aaf15c-f53e-4690-b461-148418e15598" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_f6f78a2f-6129-4c77-a4e6-97addb094b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredOther1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_87daeb52-fe16-49e3-9dd9-1268f93f6541" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_f6f78a2f-6129-4c77-a4e6-97addb094b5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_03cd05fb-f8af-4fb3-9fb6-22ad6525e464" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_87daeb52-fe16-49e3-9dd9-1268f93f6541" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_03cd05fb-f8af-4fb3-9fb6-22ad6525e464" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_580c3ee3-b9aa-4e85-9fd5-b0d17bc23b36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_87daeb52-fe16-49e3-9dd9-1268f93f6541" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_580c3ee3-b9aa-4e85-9fd5-b0d17bc23b36" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f78c302f-6f30-489c-9249-6dc4b031b9f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f78c302f-6f30-489c-9249-6dc4b031b9f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityEquityAxis_0f703436-4939-4437-9da8-64e00477d5a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OptionIndexedToIssuersEquityEquityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f78c302f-6f30-489c-9249-6dc4b031b9f9" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityEquityAxis_0f703436-4939-4437-9da8-64e00477d5a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_0f703436-4939-4437-9da8-64e00477d5a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityEquityAxis_0f703436-4939-4437-9da8-64e00477d5a8" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_0f703436-4939-4437-9da8-64e00477d5a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_014a6e36-09ea-4514-abc4-9a6d35c0cd66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityEquityAxis_0f703436-4939-4437-9da8-64e00477d5a8" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_014a6e36-09ea-4514-abc4-9a6d35c0cd66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CallOptionMember_ace7500a-012b-4385-a0af-9a17bce2efe4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CallOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_014a6e36-09ea-4514-abc4-9a6d35c0cd66" xlink:to="loc_us-gaap_CallOptionMember_ace7500a-012b-4385-a0af-9a17bce2efe4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_a1c89bd4-49ec-47b6-a042-cf54eaa8bbc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f78c302f-6f30-489c-9249-6dc4b031b9f9" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_a1c89bd4-49ec-47b6-a042-cf54eaa8bbc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_a1c89bd4-49ec-47b6-a042-cf54eaa8bbc0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_a1c89bd4-49ec-47b6-a042-cf54eaa8bbc0" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_a1c89bd4-49ec-47b6-a042-cf54eaa8bbc0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_e98f03af-98df-4e52-aa91-237e9980bc86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_a1c89bd4-49ec-47b6-a042-cf54eaa8bbc0" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_e98f03af-98df-4e52-aa91-237e9980bc86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout1Member_c2987300-e92d-47db-9839-cd8031eb0232" xlink:href="qtrx-20250630.xsd#qtrx_Earnout1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_e98f03af-98df-4e52-aa91-237e9980bc86" xlink:to="loc_qtrx_Earnout1Member_c2987300-e92d-47db-9839-cd8031eb0232" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout2Member_399bfcce-3784-4efa-a2b9-7ad44ca2397f" xlink:href="qtrx-20250630.xsd#qtrx_Earnout2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_e98f03af-98df-4e52-aa91-237e9980bc86" xlink:to="loc_qtrx_Earnout2Member_399bfcce-3784-4efa-a2b9-7ad44ca2397f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_4b034699-b9fb-4ae0-b7fb-e64aa4c98882" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f78c302f-6f30-489c-9249-6dc4b031b9f9" xlink:to="loc_srt_RangeAxis_4b034699-b9fb-4ae0-b7fb-e64aa4c98882" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4b034699-b9fb-4ae0-b7fb-e64aa4c98882_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_4b034699-b9fb-4ae0-b7fb-e64aa4c98882" xlink:to="loc_srt_RangeMember_4b034699-b9fb-4ae0-b7fb-e64aa4c98882_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7769405d-a081-479f-a8f0-c5754eb334cc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_4b034699-b9fb-4ae0-b7fb-e64aa4c98882" xlink:to="loc_srt_RangeMember_7769405d-a081-479f-a8f0-c5754eb334cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_1b45749b-7519-4d83-bc01-4cff6d5440cb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_7769405d-a081-479f-a8f0-c5754eb334cc" xlink:to="loc_srt_MinimumMember_1b45749b-7519-4d83-bc01-4cff6d5440cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_7a52e8f0-75dc-4dba-ab35-b8125c73723b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_7769405d-a081-479f-a8f0-c5754eb334cc" xlink:to="loc_srt_MaximumMember_7a52e8f0-75dc-4dba-ab35-b8125c73723b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_a6f5b6d0-a07c-45b1-baba-afe61d43457d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f78c302f-6f30-489c-9249-6dc4b031b9f9" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_a6f5b6d0-a07c-45b1-baba-afe61d43457d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a6f5b6d0-a07c-45b1-baba-afe61d43457d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_a6f5b6d0-a07c-45b1-baba-afe61d43457d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a6f5b6d0-a07c-45b1-baba-afe61d43457d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fa54ecea-9148-48fc-a119-cd49035a7a1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_a6f5b6d0-a07c-45b1-baba-afe61d43457d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fa54ecea-9148-48fc-a119-cd49035a7a1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_5e05fd85-128b-4a68-ae7d-da29ec17c027" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fa54ecea-9148-48fc-a119-cd49035a7a1e" xlink:to="loc_qtrx_EmissionInc.Member_5e05fd85-128b-4a68-ae7d-da29ec17c027" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NumberOfContingentConsiderationArrangements_dff6648b-a860-4819-aa54-dcb6fbe2e83e" xlink:href="qtrx-20250630.xsd#qtrx_NumberOfContingentConsiderationArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_qtrx_NumberOfContingentConsiderationArrangements_dff6648b-a860-4819-aa54-dcb6fbe2e83e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_ee283f1e-2cd3-4856-9bc5-74b516c55fec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_ee283f1e-2cd3-4856-9bc5-74b516c55fec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationContingentConsiderationPerformancePeriod_6bb8851d-d2d3-4814-a3cd-da2cec768232" xlink:href="qtrx-20250630.xsd#qtrx_BusinessCombinationContingentConsiderationPerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_qtrx_BusinessCombinationContingentConsiderationPerformancePeriod_6bb8851d-d2d3-4814-a3cd-da2cec768232" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_e5117454-bbcf-42cb-afe3-fa640edee0b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_e5117454-bbcf-42cb-afe3-fa640edee0b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquitySettlementAlternativesCashAtFairValue_626937dd-661b-4e45-bf19-2d9fef4be9b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OptionIndexedToIssuersEquitySettlementAlternativesCashAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquitySettlementAlternativesCashAtFairValue_626937dd-661b-4e45-bf19-2d9fef4be9b1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OptionContractIndexedToEquityPeriod_57ed4c50-6488-4b05-85d4-c35298c7fab4" xlink:href="qtrx-20250630.xsd#qtrx_OptionContractIndexedToEquityPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_qtrx_OptionContractIndexedToEquityPeriod_57ed4c50-6488-4b05-85d4-c35298c7fab4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OptionIndexedToIssuersEquityRedemptionRequirementRevenueThreshold_04d38e7d-a147-46bd-8cdc-16ea05d3bf3e" xlink:href="qtrx-20250630.xsd#qtrx_OptionIndexedToIssuersEquityRedemptionRequirementRevenueThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c27209c8-4f59-4708-aa92-96757174d185" xlink:to="loc_qtrx_OptionIndexedToIssuersEquityRedemptionRequirementRevenueThreshold_04d38e7d-a147-46bd-8cdc-16ea05d3bf3e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsSchedulethePreliminaryAllocationofthePurchasePriceDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#AcquisitionsSchedulethePreliminaryAllocationofthePurchasePriceDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/AcquisitionsSchedulethePreliminaryAllocationofthePurchasePriceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_c7729397-5c54-446c-8449-a6014ae8238e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_231327ba-c1db-4820-8cf9-6f754721d216" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c7729397-5c54-446c-8449-a6014ae8238e" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_231327ba-c1db-4820-8cf9-6f754721d216" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_7738f4a4-ed2e-4117-9e30-6b99298781b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_231327ba-c1db-4820-8cf9-6f754721d216" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_7738f4a4-ed2e-4117-9e30-6b99298781b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7738f4a4-ed2e-4117-9e30-6b99298781b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_7738f4a4-ed2e-4117-9e30-6b99298781b0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7738f4a4-ed2e-4117-9e30-6b99298781b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c9687f2b-0d33-4048-a3cc-0a1066b4a1a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_7738f4a4-ed2e-4117-9e30-6b99298781b0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c9687f2b-0d33-4048-a3cc-0a1066b4a1a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_8c4fbcff-ae59-45cd-84d2-5dca0fa775b4" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c9687f2b-0d33-4048-a3cc-0a1066b4a1a3" xlink:to="loc_qtrx_EmissionInc.Member_8c4fbcff-ae59-45cd-84d2-5dca0fa775b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c7729397-5c54-446c-8449-a6014ae8238e" xlink:to="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_9dbb87cb-15d6-4f02-85c7-2f137231d231" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_9dbb87cb-15d6-4f02-85c7-2f137231d231" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_2cccbb37-62e0-4779-b6b9-499ef7321f9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_2cccbb37-62e0-4779-b6b9-499ef7321f9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_efb74cc2-2a98-431d-948c-b1060a8a8c48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_efb74cc2-2a98-431d-948c-b1060a8a8c48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_87ea6180-42da-44c0-b18f-951cd0c1de85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_87ea6180-42da-44c0-b18f-951cd0c1de85" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_674ca47f-0798-44c3-b232-aa670263f377" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_f20e6ce7-b25f-4437-9f68-ae5d6fce74bc" xlink:to="loc_us-gaap_Goodwill_674ca47f-0798-44c3-b232-aa670263f377" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_2bab4c40-0258-4a0b-86c9-b88823727bc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c7729397-5c54-446c-8449-a6014ae8238e" xlink:to="loc_us-gaap_LiabilitiesAbstract_2bab4c40-0258-4a0b-86c9-b88823727bc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_5ff9372a-d109-4c38-b85f-f039a59a8f86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_2bab4c40-0258-4a0b-86c9-b88823727bc7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_5ff9372a-d109-4c38-b85f-f039a59a8f86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_e0211e0b-4384-4b45-8d47-2d0976aaee9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_2bab4c40-0258-4a0b-86c9-b88823727bc7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_e0211e0b-4384-4b45-8d47-2d0976aaee9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_da97851c-3c81-46c7-87a5-4c81e08776c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c7729397-5c54-446c-8449-a6014ae8238e" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_da97851c-3c81-46c7-87a5-4c81e08776c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_0a7d7c0b-e373-4c4f-9769-822a7bcdd95f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c7729397-5c54-446c-8449-a6014ae8238e" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_0a7d7c0b-e373-4c4f-9769-822a7bcdd95f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/GoodwillandIntangibleAssetsSummaryofIntangibleAssetsDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#GoodwillandIntangibleAssetsSummaryofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/GoodwillandIntangibleAssetsSummaryofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_fa38b65c-385d-45de-b7f2-d231ffd8f5e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_fa38b65c-385d-45de-b7f2-d231ffd8f5e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dfe5eaf2-d2d8-4d49-9a69-aaa1b1280631" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_fa38b65c-385d-45de-b7f2-d231ffd8f5e5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dfe5eaf2-d2d8-4d49-9a69-aaa1b1280631" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_dfe5eaf2-d2d8-4d49-9a69-aaa1b1280631_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dfe5eaf2-d2d8-4d49-9a69-aaa1b1280631" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_dfe5eaf2-d2d8-4d49-9a69-aaa1b1280631_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dfe5eaf2-d2d8-4d49-9a69-aaa1b1280631" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_KnowHowMember_4af7c013-26d0-49c1-ac96-00f52f5ee134" xlink:href="qtrx-20250630.xsd#qtrx_KnowHowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:to="loc_qtrx_KnowHowMember_4af7c013-26d0-49c1-ac96-00f52f5ee134" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_e4022ee9-f6e7-4e61-8bdd-18cc24bf30a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_e4022ee9-f6e7-4e61-8bdd-18cc24bf30a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_31925ce0-dc5c-4bf4-8123-1c2f9c3d254c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:to="loc_us-gaap_CustomerRelationshipsMember_31925ce0-dc5c-4bf4-8123-1c2f9c3d254c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_738ca51a-e98c-43ed-b0ee-7f43bd6dcd33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_738ca51a-e98c-43ed-b0ee-7f43bd6dcd33" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_d58b762b-d7ce-495b-a645-da107764a520" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2f60c039-9baa-4894-ab36-8690039cc38f" xlink:to="loc_us-gaap_TradeNamesMember_d58b762b-d7ce-495b-a645-da107764a520" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_11cbdc60-1fd7-4668-9463-f7c8ea594965" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_fa38b65c-385d-45de-b7f2-d231ffd8f5e5" xlink:to="loc_srt_RangeAxis_11cbdc60-1fd7-4668-9463-f7c8ea594965" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_11cbdc60-1fd7-4668-9463-f7c8ea594965_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_11cbdc60-1fd7-4668-9463-f7c8ea594965" xlink:to="loc_srt_RangeMember_11cbdc60-1fd7-4668-9463-f7c8ea594965_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_431f5cf1-43f8-4bbb-989b-b11638318c38" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_11cbdc60-1fd7-4668-9463-f7c8ea594965" xlink:to="loc_srt_RangeMember_431f5cf1-43f8-4bbb-989b-b11638318c38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3f814fef-cfe8-4a66-864c-6cb376ac1de4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_431f5cf1-43f8-4bbb-989b-b11638318c38" xlink:to="loc_srt_MinimumMember_3f814fef-cfe8-4a66-864c-6cb376ac1de4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_c09f6568-66b9-47d3-a767-65687154a7d4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_431f5cf1-43f8-4bbb-989b-b11638318c38" xlink:to="loc_srt_MaximumMember_c09f6568-66b9-47d3-a767-65687154a7d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_f603fbad-5243-490d-aeb2-90e34ce41b06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_f603fbad-5243-490d-aeb2-90e34ce41b06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_f8b64e14-7700-4f92-9307-645a6b498fc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_f8b64e14-7700-4f92-9307-645a6b498fc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_6a3a78e9-ef7e-4ec8-a60c-6cfcb889ba25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_6a3a78e9-ef7e-4ec8-a60c-6cfcb889ba25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments_8c8b8046-d15a-4266-9ec8-a2988d2f50d8" xlink:href="qtrx-20250630.xsd#qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments_8c8b8046-d15a-4266-9ec8-a2988d2f50d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_15834015-18fa-408d-8ae8-da40c6f48841" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_15834015-18fa-408d-8ae8-da40c6f48841" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_081beba7-7c23-449d-9f8e-69c01674b6b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_3eaffffb-e366-42eb-9df1-28fe524f2835" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_081beba7-7c23-449d-9f8e-69c01674b6b9" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RevenueandRelatedMattersDisaggregatedRevenueDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#RevenueandRelatedMattersDisaggregatedRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/RevenueandRelatedMattersDisaggregatedRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_c4411bfe-207e-4d1d-bf68-da4a327ee087" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_6f9af051-edfa-4df0-96ca-c9f1bdab17ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_c4411bfe-207e-4d1d-bf68-da4a327ee087" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_6f9af051-edfa-4df0-96ca-c9f1bdab17ab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_79fdd1ab-e318-4bee-8932-d062a9f8dceb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_6f9af051-edfa-4df0-96ca-c9f1bdab17ab" xlink:to="loc_srt_ProductOrServiceAxis_79fdd1ab-e318-4bee-8932-d062a9f8dceb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_79fdd1ab-e318-4bee-8932-d062a9f8dceb_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_79fdd1ab-e318-4bee-8932-d062a9f8dceb" xlink:to="loc_srt_ProductsAndServicesDomain_79fdd1ab-e318-4bee-8932-d062a9f8dceb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_81de2c94-3f12-40f2-8eaf-ff559c0b7fc5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_79fdd1ab-e318-4bee-8932-d062a9f8dceb" xlink:to="loc_srt_ProductsAndServicesDomain_81de2c94-3f12-40f2-8eaf-ff559c0b7fc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_6ed990b0-5a25-463f-a94e-c1cbd85ec7c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_81de2c94-3f12-40f2-8eaf-ff559c0b7fc5" xlink:to="loc_us-gaap_ProductMember_6ed990b0-5a25-463f-a94e-c1cbd85ec7c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_InstrumentsMember_25195cc0-03ef-46fb-90c4-e783ed6802c8" xlink:href="qtrx-20250630.xsd#qtrx_InstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_6ed990b0-5a25-463f-a94e-c1cbd85ec7c8" xlink:to="loc_qtrx_InstrumentsMember_25195cc0-03ef-46fb-90c4-e783ed6802c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ConsumableAndOtherProductsMember_1f3bdd20-88ee-4b2d-8997-7b676a7b89fd" xlink:href="qtrx-20250630.xsd#qtrx_ConsumableAndOtherProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_6ed990b0-5a25-463f-a94e-c1cbd85ec7c8" xlink:to="loc_qtrx_ConsumableAndOtherProductsMember_1f3bdd20-88ee-4b2d-8997-7b676a7b89fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceAndOtherRevenueMember_cf884f69-4840-49f4-98b6-84c1639532b1" xlink:href="qtrx-20250630.xsd#qtrx_ServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_81de2c94-3f12-40f2-8eaf-ff559c0b7fc5" xlink:to="loc_qtrx_ServiceAndOtherRevenueMember_cf884f69-4840-49f4-98b6-84c1639532b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ResearchServicesMember_8869421e-a906-485c-8956-a51ea9433296" xlink:href="qtrx-20250630.xsd#qtrx_ResearchServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_cf884f69-4840-49f4-98b6-84c1639532b1" xlink:to="loc_qtrx_ResearchServicesMember_8869421e-a906-485c-8956-a51ea9433296" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceTypeWarrantiesMember_30b0531e-69d1-48ed-a5a8-6d85c0d107c3" xlink:href="qtrx-20250630.xsd#qtrx_ServiceTypeWarrantiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_cf884f69-4840-49f4-98b6-84c1639532b1" xlink:to="loc_qtrx_ServiceTypeWarrantiesMember_30b0531e-69d1-48ed-a5a8-6d85c0d107c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OtherServicesMember_c980b850-cb9e-44e8-9623-fb3371fb7fe3" xlink:href="qtrx-20250630.xsd#qtrx_OtherServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_cf884f69-4840-49f4-98b6-84c1639532b1" xlink:to="loc_qtrx_OtherServicesMember_c980b850-cb9e-44e8-9623-fb3371fb7fe3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseAndServiceMember_19b692f0-1b4c-4cb3-9e49-8764fc8db362" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicenseAndServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_81de2c94-3f12-40f2-8eaf-ff559c0b7fc5" xlink:to="loc_us-gaap_LicenseAndServiceMember_19b692f0-1b4c-4cb3-9e49-8764fc8db362" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_5b31cdb1-8833-4a45-aff5-f816eaac97ee" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_6f9af051-edfa-4df0-96ca-c9f1bdab17ab" xlink:to="loc_srt_StatementGeographicalAxis_5b31cdb1-8833-4a45-aff5-f816eaac97ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_5b31cdb1-8833-4a45-aff5-f816eaac97ee_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_5b31cdb1-8833-4a45-aff5-f816eaac97ee" xlink:to="loc_srt_SegmentGeographicalDomain_5b31cdb1-8833-4a45-aff5-f816eaac97ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_fcf170be-e293-4669-8682-ff454c2078b4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_5b31cdb1-8833-4a45-aff5-f816eaac97ee" xlink:to="loc_srt_SegmentGeographicalDomain_fcf170be-e293-4669-8682-ff454c2078b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_b62123b9-9f60-4c20-89ea-06f3152346cf" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fcf170be-e293-4669-8682-ff454c2078b4" xlink:to="loc_srt_NorthAmericaMember_b62123b9-9f60-4c20-89ea-06f3152346cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_c73e88ba-4f65-43d7-8d2a-e27a5e00c64a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fcf170be-e293-4669-8682-ff454c2078b4" xlink:to="loc_us-gaap_EMEAMember_c73e88ba-4f65-43d7-8d2a-e27a5e00c64a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_9fa9bc22-aeec-4d1a-a8f6-42405d7d6915" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fcf170be-e293-4669-8682-ff454c2078b4" xlink:to="loc_srt_AsiaPacificMember_9fa9bc22-aeec-4d1a-a8f6-42405d7d6915" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_34cfcb37-637a-414c-a832-201ec92e9be0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_c4411bfe-207e-4d1d-bf68-da4a327ee087" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_34cfcb37-637a-414c-a832-201ec92e9be0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RevenueandRelatedMattersNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#RevenueandRelatedMattersNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/RevenueandRelatedMattersNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_c1651762-6384-4181-9858-16a539c6c4c8_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:to="loc_srt_NameOfMajorCustomerDomain_c1651762-6384-4181-9858-16a539c6c4c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_cc91a78d-86a1-44cf-a268-fc04fc048996" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:to="loc_srt_NameOfMajorCustomerDomain_cc91a78d-86a1-44cf-a268-fc04fc048996" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_CustomerMember_c43cb8ac-338d-4e52-b63d-35d2e74befba" xlink:href="qtrx-20250630.xsd#qtrx_CustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_cc91a78d-86a1-44cf-a268-fc04fc048996" xlink:to="loc_qtrx_CustomerMember_c43cb8ac-338d-4e52-b63d-35d2e74befba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_cb486a19-36dc-4b94-82f7-4509bb97cb36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_cb486a19-36dc-4b94-82f7-4509bb97cb36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_4d86e8c1-2a84-47b4-8503-b70db16816c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:to="loc_us-gaap_SalesRevenueNetMember_4d86e8c1-2a84-47b4-8503-b70db16816c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_27c18014-e976-4241-92b3-2af79ed380ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:to="loc_us-gaap_AccountsReceivableMember_27c18014-e976-4241-92b3-2af79ed380ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ff9ff412-ab8d-4d0e-be32-5aca9f124214_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ff9ff412-ab8d-4d0e-be32-5aca9f124214_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_f014bdf5-a907-4538-acc7-a478c2313e12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_f014bdf5-a907-4538-acc7-a478c2313e12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_83e669c8-6f5b-4e9e-846a-0c96aa185f06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_f014bdf5-a907-4538-acc7-a478c2313e12" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_83e669c8-6f5b-4e9e-846a-0c96aa185f06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_681bea36-71ad-444e-b556-1af54a3de6f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_681bea36-71ad-444e-b556-1af54a3de6f8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5b170b5c-b307-4a8c-8278-33b43fe543c1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:to="loc_srt_ProductsAndServicesDomain_5b170b5c-b307-4a8c-8278-33b43fe543c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_65aff5c3-acee-47bd-ad77-fe826941fa49" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:to="loc_srt_ProductsAndServicesDomain_65aff5c3-acee-47bd-ad77-fe826941fa49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_d4b63cea-c8c4-4745-9440-4afd7709aa32" xlink:href="qtrx-20250630.xsd#qtrx_UndeliveredLicensesOfIntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_65aff5c3-acee-47bd-ad77-fe826941fa49" xlink:to="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_d4b63cea-c8c4-4745-9440-4afd7709aa32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_f6ef358c-6c2d-4f8a-b86a-db3618cd6897_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_f6ef358c-6c2d-4f8a-b86a-db3618cd6897_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_c4c371e7-8440-4320-9553-8c0dfe02faa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_c4c371e7-8440-4320-9553-8c0dfe02faa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NationalInstitutesOfHealthMember_53213da0-ccda-4f7b-a565-bbd5a5418609" xlink:href="qtrx-20250630.xsd#qtrx_NationalInstitutesOfHealthMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_c4c371e7-8440-4320-9553-8c0dfe02faa1" xlink:to="loc_qtrx_NationalInstitutesOfHealthMember_53213da0-ccda-4f7b-a565-bbd5a5418609" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NumberOfCustomersWithHighPercentOfTotalRevenue_92163794-ed95-4d08-a915-4d24829db69e" xlink:href="qtrx-20250630.xsd#qtrx_NumberOfCustomersWithHighPercentOfTotalRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_NumberOfCustomersWithHighPercentOfTotalRevenue_92163794-ed95-4d08-a915-4d24829db69e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_ccb03680-3ccf-41d4-9dc1-a587da0a2d6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_ccb03680-3ccf-41d4-9dc1-a587da0a2d6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NumberOfCustomersWithHighPercentOfGrossAccountsReceivable_1ac01f35-50c2-460e-b313-20b0777194f7" xlink:href="qtrx-20250630.xsd#qtrx_NumberOfCustomersWithHighPercentOfGrossAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_NumberOfCustomersWithHighPercentOfGrossAccountsReceivable_1ac01f35-50c2-460e-b313-20b0777194f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_cec3cad1-51c5-4dfe-82e9-abe79f6a63b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_cec3cad1-51c5-4dfe-82e9-abe79f6a63b4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cd050d4c-b014-4cd4-af73-01bf8c9ef50c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cd050d4c-b014-4cd4-af73-01bf8c9ef50c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_b68759d5-0f26-4b98-979a-899e03bb4bdd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_b68759d5-0f26-4b98-979a-899e03bb4bdd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_200cd549-c7cb-4989-b218-06afbaf4f610" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_200cd549-c7cb-4989-b218-06afbaf4f610" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostImpairmentLoss_44495e82-b41e-442a-a383-758b314a3ee4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_CapitalizedContractCostImpairmentLoss_44495e82-b41e-442a-a383-758b314a3ee4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ContractValue_7fe4e712-9e6b-468e-bdec-69d70904cda4" xlink:href="qtrx-20250630.xsd#qtrx_ContractValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_ContractValue_7fe4e712-9e6b-468e-bdec-69d70904cda4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_GrantsReceived_c77aa30b-8e57-4820-9a25-f1bbfb9125af" xlink:href="qtrx-20250630.xsd#qtrx_GrantsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_GrantsReceived_c77aa30b-8e57-4820-9a25-f1bbfb9125af" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f9cc6d6b-1467-4b94-8669-8411b73b06a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f9cc6d6b-1467-4b94-8669-8411b73b06a6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_63932a54-21f6-428b-a18a-d9546e171bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_63932a54-21f6-428b-a18a-d9546e171bc9" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RevenueandRelatedMattersNarrativeDetails_1" xlink:type="simple" xlink:href="qtrx-20250630.xsd#RevenueandRelatedMattersNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/RevenueandRelatedMattersNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_c1651762-6384-4181-9858-16a539c6c4c8_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:to="loc_srt_NameOfMajorCustomerDomain_c1651762-6384-4181-9858-16a539c6c4c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_cc91a78d-86a1-44cf-a268-fc04fc048996" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_c1651762-6384-4181-9858-16a539c6c4c8" xlink:to="loc_srt_NameOfMajorCustomerDomain_cc91a78d-86a1-44cf-a268-fc04fc048996" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_CustomerMember_c43cb8ac-338d-4e52-b63d-35d2e74befba" xlink:href="qtrx-20250630.xsd#qtrx_CustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_cc91a78d-86a1-44cf-a268-fc04fc048996" xlink:to="loc_qtrx_CustomerMember_c43cb8ac-338d-4e52-b63d-35d2e74befba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_cb486a19-36dc-4b94-82f7-4509bb97cb36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_cb486a19-36dc-4b94-82f7-4509bb97cb36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_cb486a19-36dc-4b94-82f7-4509bb97cb36" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_4d86e8c1-2a84-47b4-8503-b70db16816c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:to="loc_us-gaap_SalesRevenueNetMember_4d86e8c1-2a84-47b4-8503-b70db16816c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_27c18014-e976-4241-92b3-2af79ed380ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d8112673-812b-4339-9b6e-cad9949e90c8" xlink:to="loc_us-gaap_AccountsReceivableMember_27c18014-e976-4241-92b3-2af79ed380ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ff9ff412-ab8d-4d0e-be32-5aca9f124214_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ff9ff412-ab8d-4d0e-be32-5aca9f124214_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_f014bdf5-a907-4538-acc7-a478c2313e12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_ff9ff412-ab8d-4d0e-be32-5aca9f124214" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_f014bdf5-a907-4538-acc7-a478c2313e12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_83e669c8-6f5b-4e9e-846a-0c96aa185f06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_f014bdf5-a907-4538-acc7-a478c2313e12" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_83e669c8-6f5b-4e9e-846a-0c96aa185f06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5b170b5c-b307-4a8c-8278-33b43fe543c1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:to="loc_srt_ProductsAndServicesDomain_5b170b5c-b307-4a8c-8278-33b43fe543c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_65aff5c3-acee-47bd-ad77-fe826941fa49" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_5b170b5c-b307-4a8c-8278-33b43fe543c1" xlink:to="loc_srt_ProductsAndServicesDomain_65aff5c3-acee-47bd-ad77-fe826941fa49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_d4b63cea-c8c4-4745-9440-4afd7709aa32" xlink:href="qtrx-20250630.xsd#qtrx_UndeliveredLicensesOfIntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_65aff5c3-acee-47bd-ad77-fe826941fa49" xlink:to="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_d4b63cea-c8c4-4745-9440-4afd7709aa32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_f043f6b5-ba78-4d3e-97fc-3e9c60a621c7" xlink:to="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_f6ef358c-6c2d-4f8a-b86a-db3618cd6897_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_f6ef358c-6c2d-4f8a-b86a-db3618cd6897_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_c4c371e7-8440-4320-9553-8c0dfe02faa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_f6ef358c-6c2d-4f8a-b86a-db3618cd6897" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_c4c371e7-8440-4320-9553-8c0dfe02faa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NationalInstitutesOfHealthMember_53213da0-ccda-4f7b-a565-bbd5a5418609" xlink:href="qtrx-20250630.xsd#qtrx_NationalInstitutesOfHealthMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_c4c371e7-8440-4320-9553-8c0dfe02faa1" xlink:to="loc_qtrx_NationalInstitutesOfHealthMember_53213da0-ccda-4f7b-a565-bbd5a5418609" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NumberOfCustomersWithHighPercentOfTotalRevenue_92163794-ed95-4d08-a915-4d24829db69e" xlink:href="qtrx-20250630.xsd#qtrx_NumberOfCustomersWithHighPercentOfTotalRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_NumberOfCustomersWithHighPercentOfTotalRevenue_92163794-ed95-4d08-a915-4d24829db69e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_ccb03680-3ccf-41d4-9dc1-a587da0a2d6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_ccb03680-3ccf-41d4-9dc1-a587da0a2d6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NumberOfCustomersWithHighPercentOfGrossAccountsReceivable_1ac01f35-50c2-460e-b313-20b0777194f7" xlink:href="qtrx-20250630.xsd#qtrx_NumberOfCustomersWithHighPercentOfGrossAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_NumberOfCustomersWithHighPercentOfGrossAccountsReceivable_1ac01f35-50c2-460e-b313-20b0777194f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_cec3cad1-51c5-4dfe-82e9-abe79f6a63b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_cec3cad1-51c5-4dfe-82e9-abe79f6a63b4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cd050d4c-b014-4cd4-af73-01bf8c9ef50c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_cd050d4c-b014-4cd4-af73-01bf8c9ef50c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_b68759d5-0f26-4b98-979a-899e03bb4bdd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_b68759d5-0f26-4b98-979a-899e03bb4bdd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_200cd549-c7cb-4989-b218-06afbaf4f610" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_200cd549-c7cb-4989-b218-06afbaf4f610" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostImpairmentLoss_44495e82-b41e-442a-a383-758b314a3ee4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_CapitalizedContractCostImpairmentLoss_44495e82-b41e-442a-a383-758b314a3ee4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ContractValue_7fe4e712-9e6b-468e-bdec-69d70904cda4" xlink:href="qtrx-20250630.xsd#qtrx_ContractValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_ContractValue_7fe4e712-9e6b-468e-bdec-69d70904cda4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_GrantsReceived_c77aa30b-8e57-4820-9a25-f1bbfb9125af" xlink:href="qtrx-20250630.xsd#qtrx_GrantsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_qtrx_GrantsReceived_c77aa30b-8e57-4820-9a25-f1bbfb9125af" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f9cc6d6b-1467-4b94-8669-8411b73b06a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f9cc6d6b-1467-4b94-8669-8411b73b06a6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_63932a54-21f6-428b-a18a-d9546e171bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_48de632f-31ee-4797-b8a4-a1d88aaf08fb" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_63932a54-21f6-428b-a18a-d9546e171bc9" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/MarketableSecuritiesSummaryofAmortizedCostGrossUnrealizedGainsGrossUnrealizedLossesandFairValueDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#MarketableSecuritiesSummaryofAmortizedCostGrossUnrealizedGainsGrossUnrealizedLossesandFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/MarketableSecuritiesSummaryofAmortizedCostGrossUnrealizedGainsGrossUnrealizedLossesandFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_653e6024-f91e-4813-b6ee-ef11f5a3817f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_1074c81e-db76-4029-b6d7-500362b712b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_653e6024-f91e-4813-b6ee-ef11f5a3817f" xlink:to="loc_us-gaap_MarketableSecuritiesTable_1074c81e-db76-4029-b6d7-500362b712b7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_9a9f9fae-12ef-46e7-9853-f0c3d8aa6bab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_1074c81e-db76-4029-b6d7-500362b712b7" xlink:to="loc_us-gaap_FinancialInstrumentAxis_9a9f9fae-12ef-46e7-9853-f0c3d8aa6bab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_9a9f9fae-12ef-46e7-9853-f0c3d8aa6bab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_9a9f9fae-12ef-46e7-9853-f0c3d8aa6bab" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_9a9f9fae-12ef-46e7-9853-f0c3d8aa6bab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_95e48ba6-9d63-4b38-8288-f8fe8930e81f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_9a9f9fae-12ef-46e7-9853-f0c3d8aa6bab" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_95e48ba6-9d63-4b38-8288-f8fe8930e81f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_f6c8b95e-25e9-444c-a34d-a94395c33233" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_95e48ba6-9d63-4b38-8288-f8fe8930e81f" xlink:to="loc_us-gaap_CommercialPaperMember_f6c8b95e-25e9-444c-a34d-a94395c33233" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_2103f15a-f9e3-47a1-a3da-806d57806971" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_95e48ba6-9d63-4b38-8288-f8fe8930e81f" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_2103f15a-f9e3-47a1-a3da-806d57806971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_687c7305-bdb0-4be8-a1a9-7150d3182be5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_95e48ba6-9d63-4b38-8288-f8fe8930e81f" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_687c7305-bdb0-4be8-a1a9-7150d3182be5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_42ff700b-24ed-4b44-8ee1-f05a701dae2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_95e48ba6-9d63-4b38-8288-f8fe8930e81f" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_42ff700b-24ed-4b44-8ee1-f05a701dae2f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss_541693d8-8275-47a0-92d6-c06a51c646f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_653e6024-f91e-4813-b6ee-ef11f5a3817f" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss_541693d8-8275-47a0-92d6-c06a51c646f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain_e2bdea06-60e9-46c8-9e40-562f2f03b0a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_653e6024-f91e-4813-b6ee-ef11f5a3817f" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain_e2bdea06-60e9-46c8-9e40-562f2f03b0a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss_6b1a3989-475c-40ac-8a0f-949aea01793f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_653e6024-f91e-4813-b6ee-ef11f5a3817f" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss_6b1a3989-475c-40ac-8a0f-949aea01793f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue_54c17423-6936-45c9-9f68-aed0ce4ff748" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_653e6024-f91e-4813-b6ee-ef11f5a3817f" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue_54c17423-6936-45c9-9f68-aed0ce4ff748" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/MarketableSecuritiesSummaryofFairValueandGrossUnrealizedLossesDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#MarketableSecuritiesSummaryofFairValueandGrossUnrealizedLossesDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/MarketableSecuritiesSummaryofFairValueandGrossUnrealizedLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_76362e97-c4ba-4297-be3a-3af8b16a363c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_b6fb601c-3303-4185-8bcc-f975149545d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_76362e97-c4ba-4297-be3a-3af8b16a363c" xlink:to="loc_us-gaap_MarketableSecuritiesTable_b6fb601c-3303-4185-8bcc-f975149545d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_4d0d2e05-02ff-4039-925c-3cc6bd875ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_b6fb601c-3303-4185-8bcc-f975149545d5" xlink:to="loc_us-gaap_FinancialInstrumentAxis_4d0d2e05-02ff-4039-925c-3cc6bd875ebf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4d0d2e05-02ff-4039-925c-3cc6bd875ebf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_4d0d2e05-02ff-4039-925c-3cc6bd875ebf" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4d0d2e05-02ff-4039-925c-3cc6bd875ebf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7ae0e9a4-b381-4ca3-a564-ef45b34424f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_4d0d2e05-02ff-4039-925c-3cc6bd875ebf" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7ae0e9a4-b381-4ca3-a564-ef45b34424f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_599922cb-be8f-4f38-b2c9-bdeeaa109839" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7ae0e9a4-b381-4ca3-a564-ef45b34424f0" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_599922cb-be8f-4f38-b2c9-bdeeaa109839" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_e295b76f-e21d-4e03-a5ad-fe487682d1e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7ae0e9a4-b381-4ca3-a564-ef45b34424f0" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_e295b76f-e21d-4e03-a5ad-fe487682d1e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_eb49a16b-b41d-4ea8-bb6b-6927f6ab979a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7ae0e9a4-b381-4ca3-a564-ef45b34424f0" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_eb49a16b-b41d-4ea8-bb6b-6927f6ab979a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_254d6558-5faf-4e91-bae9-6b32f787b92a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_76362e97-c4ba-4297-be3a-3af8b16a363c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_254d6558-5faf-4e91-bae9-6b32f787b92a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_ab2d587a-f9b5-41e5-9d5c-b271b754b0ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_76362e97-c4ba-4297-be3a-3af8b16a363c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_ab2d587a-f9b5-41e5-9d5c-b271b754b0ee" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_745839b2-a764-4779-b286-61648de44e81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_4df0ab6d-877d-448f-9392-2eb7d35579f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_745839b2-a764-4779-b286-61648de44e81" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_4df0ab6d-877d-448f-9392-2eb7d35579f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8dcc9ba-83ff-4a04-ac76-25732bff23fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_4df0ab6d-877d-448f-9392-2eb7d35579f0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8dcc9ba-83ff-4a04-ac76-25732bff23fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d8dcc9ba-83ff-4a04-ac76-25732bff23fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8dcc9ba-83ff-4a04-ac76-25732bff23fa" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d8dcc9ba-83ff-4a04-ac76-25732bff23fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_33b4d7d6-6b08-474f-8db0-6eb212eaf4e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8dcc9ba-83ff-4a04-ac76-25732bff23fa" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_33b4d7d6-6b08-474f-8db0-6eb212eaf4e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_ce90ec2a-19c0-4177-aee5-e2dbc1676634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_33b4d7d6-6b08-474f-8db0-6eb212eaf4e8" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_ce90ec2a-19c0-4177-aee5-e2dbc1676634" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_63d0fd34-445f-4d74-9d31-1f3030f1778b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_33b4d7d6-6b08-474f-8db0-6eb212eaf4e8" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_63d0fd34-445f-4d74-9d31-1f3030f1778b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_1a2b73db-321f-404e-b4af-a4c2fd4d8aae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_33b4d7d6-6b08-474f-8db0-6eb212eaf4e8" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_1a2b73db-321f-404e-b4af-a4c2fd4d8aae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_97056dc6-6444-4ad3-ad16-237fd2244ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_4df0ab6d-877d-448f-9392-2eb7d35579f0" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_97056dc6-6444-4ad3-ad16-237fd2244ac0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_97056dc6-6444-4ad3-ad16-237fd2244ac0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_97056dc6-6444-4ad3-ad16-237fd2244ac0" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_97056dc6-6444-4ad3-ad16-237fd2244ac0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_97056dc6-6444-4ad3-ad16-237fd2244ac0" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_15e3d6a5-25a3-4b33-a5f4-89da0014a5ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:to="loc_us-gaap_MoneyMarketFundsMember_15e3d6a5-25a3-4b33-a5f4-89da0014a5ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_a5f32b97-7568-4597-a823-8d77a4c9fdfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:to="loc_us-gaap_CommercialPaperMember_a5f32b97-7568-4597-a823-8d77a4c9fdfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_46490626-1707-4f14-a6e2-8a00753f1b41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_46490626-1707-4f14-a6e2-8a00753f1b41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_810be229-7a0a-4dd6-a125-1f7f50485523" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_810be229-7a0a-4dd6-a125-1f7f50485523" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_c40c73f5-4c94-4610-a8b8-82311b691fc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_00b91d5e-53d8-473e-89f7-855003236408" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_c40c73f5-4c94-4610-a8b8-82311b691fc7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_aaa82c51-c495-4f93-bae5-a0a9ec4c0d63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_4df0ab6d-877d-448f-9392-2eb7d35579f0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_aaa82c51-c495-4f93-bae5-a0a9ec4c0d63" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_aaa82c51-c495-4f93-bae5-a0a9ec4c0d63_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_aaa82c51-c495-4f93-bae5-a0a9ec4c0d63" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_aaa82c51-c495-4f93-bae5-a0a9ec4c0d63_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_470bd1ae-93e5-4253-a806-ce6568de763e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_aaa82c51-c495-4f93-bae5-a0a9ec4c0d63" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_470bd1ae-93e5-4253-a806-ce6568de763e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_de6089cf-18d7-41c3-80e5-6aaa61acb2e8" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_470bd1ae-93e5-4253-a806-ce6568de763e" xlink:to="loc_qtrx_EmissionInc.Member_de6089cf-18d7-41c3-80e5-6aaa61acb2e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_6cd3281a-a1be-43fd-8139-8a58212ff181" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_4df0ab6d-877d-448f-9392-2eb7d35579f0" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_6cd3281a-a1be-43fd-8139-8a58212ff181" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_6cd3281a-a1be-43fd-8139-8a58212ff181_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_6cd3281a-a1be-43fd-8139-8a58212ff181" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_6cd3281a-a1be-43fd-8139-8a58212ff181_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_faacc7c6-88bd-4a17-be46-211ccf7222e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_6cd3281a-a1be-43fd-8139-8a58212ff181" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_faacc7c6-88bd-4a17-be46-211ccf7222e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout2Member_22985c5b-c0c9-4071-880b-eee737f2eb55" xlink:href="qtrx-20250630.xsd#qtrx_Earnout2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_faacc7c6-88bd-4a17-be46-211ccf7222e1" xlink:to="loc_qtrx_Earnout2Member_22985c5b-c0c9-4071-880b-eee737f2eb55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_745839b2-a764-4779-b286-61648de44e81" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_165d974c-c701-4922-9436-2d493cf4cc71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_165d974c-c701-4922-9436-2d493cf4cc71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_eda3d606-47ef-47e1-9a86-de923c9e9d72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_eda3d606-47ef-47e1-9a86-de923c9e9d72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_b0ffdb22-8014-4cad-9d74-7f86c6350a76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_b0ffdb22-8014-4cad-9d74-7f86c6350a76" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_dd0826a0-2a92-4ec0-88bd-787a7c2c07ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_dd0826a0-2a92-4ec0-88bd-787a7c2c07ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_635f6d69-9341-4d7b-b07c-01b786938a4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_17fe8ee4-b423-465a-b593-e48b7e9365ae" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_635f6d69-9341-4d7b-b07c-01b786938a4a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationContingentConsiderationPerformancePeriod_2e49dee8-0697-4f09-9488-fa0a592fe554" xlink:href="qtrx-20250630.xsd#qtrx_BusinessCombinationContingentConsiderationPerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_745839b2-a764-4779-b286-61648de44e81" xlink:to="loc_qtrx_BusinessCombinationContingentConsiderationPerformancePeriod_2e49dee8-0697-4f09-9488-fa0a592fe554" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/FairValueofFinancialInstrumentsFairValueMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#FairValueofFinancialInstrumentsFairValueMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/FairValueofFinancialInstrumentsFairValueMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_e50677c8-9e1c-49ee-acec-61270b6d1dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_90912f79-86c7-4a92-858a-3aa91538e647" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_e50677c8-9e1c-49ee-acec-61270b6d1dc5" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_90912f79-86c7-4a92-858a-3aa91538e647" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_d10bc7b4-774f-44f1-8c83-ca37e738bddb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_90912f79-86c7-4a92-858a-3aa91538e647" xlink:to="loc_srt_RangeAxis_d10bc7b4-774f-44f1-8c83-ca37e738bddb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d10bc7b4-774f-44f1-8c83-ca37e738bddb_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_d10bc7b4-774f-44f1-8c83-ca37e738bddb" xlink:to="loc_srt_RangeMember_d10bc7b4-774f-44f1-8c83-ca37e738bddb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_df7ea182-9ee3-4b10-8358-1b112a827d08" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_d10bc7b4-774f-44f1-8c83-ca37e738bddb" xlink:to="loc_srt_RangeMember_df7ea182-9ee3-4b10-8358-1b112a827d08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_6632b713-d5fd-48ce-a7ab-b3609b52032e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_df7ea182-9ee3-4b10-8358-1b112a827d08" xlink:to="loc_srt_MinimumMember_6632b713-d5fd-48ce-a7ab-b3609b52032e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_db357df0-d68e-446d-9d47-5a013ebdf46f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_df7ea182-9ee3-4b10-8358-1b112a827d08" xlink:to="loc_srt_MaximumMember_db357df0-d68e-446d-9d47-5a013ebdf46f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_62606239-0cee-4086-abbc-d4e321f0bbe3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_90912f79-86c7-4a92-858a-3aa91538e647" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_62606239-0cee-4086-abbc-d4e321f0bbe3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_62606239-0cee-4086-abbc-d4e321f0bbe3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_62606239-0cee-4086-abbc-d4e321f0bbe3" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_62606239-0cee-4086-abbc-d4e321f0bbe3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_13d5fa83-d3b3-441f-bd8f-8104c36a2cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_62606239-0cee-4086-abbc-d4e321f0bbe3" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_13d5fa83-d3b3-441f-bd8f-8104c36a2cc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_beae9cf8-fb43-4d51-973f-1421f29826fd" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_13d5fa83-d3b3-441f-bd8f-8104c36a2cc1" xlink:to="loc_qtrx_EmissionInc.Member_beae9cf8-fb43-4d51-973f-1421f29826fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_9457293c-acb1-47e5-9b3a-1d8efc174cea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_90912f79-86c7-4a92-858a-3aa91538e647" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_9457293c-acb1-47e5-9b3a-1d8efc174cea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_9457293c-acb1-47e5-9b3a-1d8efc174cea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_9457293c-acb1-47e5-9b3a-1d8efc174cea" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_9457293c-acb1-47e5-9b3a-1d8efc174cea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_c20b6fab-fcbf-43e2-ac7a-bbb3fd695d95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_9457293c-acb1-47e5-9b3a-1d8efc174cea" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_c20b6fab-fcbf-43e2-ac7a-bbb3fd695d95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout1Member_8171d70d-5d90-4a78-b199-1c3612708872" xlink:href="qtrx-20250630.xsd#qtrx_Earnout1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_c20b6fab-fcbf-43e2-ac7a-bbb3fd695d95" xlink:to="loc_qtrx_Earnout1Member_8171d70d-5d90-4a78-b199-1c3612708872" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_aed227b6-4438-44b8-8d5d-78e4e60a631d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_e50677c8-9e1c-49ee-acec-61270b6d1dc5" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_aed227b6-4438-44b8-8d5d-78e4e60a631d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#FairValueofFinancialInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7fa0485a-94df-4d98-83aa-22984fcc0e67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_f99bf67f-ecf6-4978-9c20-f2681de63ca8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7fa0485a-94df-4d98-83aa-22984fcc0e67" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_f99bf67f-ecf6-4978-9c20-f2681de63ca8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_5191221d-dee2-4be1-9275-2b7162f63799" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_f99bf67f-ecf6-4978-9c20-f2681de63ca8" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_5191221d-dee2-4be1-9275-2b7162f63799" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_5191221d-dee2-4be1-9275-2b7162f63799_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_5191221d-dee2-4be1-9275-2b7162f63799" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_5191221d-dee2-4be1-9275-2b7162f63799_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_f9b22775-fc92-4717-9939-2773e2b6c7e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_5191221d-dee2-4be1-9275-2b7162f63799" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_f9b22775-fc92-4717-9939-2773e2b6c7e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_b29ecc03-3254-4b9b-958b-4e1da65a389a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsNonrecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_f9b22775-fc92-4717-9939-2773e2b6c7e6" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_b29ecc03-3254-4b9b-958b-4e1da65a389a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_011e20c6-5681-4a95-bca9-29cca62ee68f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_f99bf67f-ecf6-4978-9c20-f2681de63ca8" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_011e20c6-5681-4a95-bca9-29cca62ee68f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_011e20c6-5681-4a95-bca9-29cca62ee68f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_011e20c6-5681-4a95-bca9-29cca62ee68f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_011e20c6-5681-4a95-bca9-29cca62ee68f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_caba4311-456f-4087-a084-fe337f5a8c2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_011e20c6-5681-4a95-bca9-29cca62ee68f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_caba4311-456f-4087-a084-fe337f5a8c2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_3c85ab7e-b9fa-4a37-bc62-00ebf86dff54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_caba4311-456f-4087-a084-fe337f5a8c2e" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_3c85ab7e-b9fa-4a37-bc62-00ebf86dff54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues_c5f50255-1ea2-42bb-bb4b-cda73cf9b9fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7fa0485a-94df-4d98-83aa-22984fcc0e67" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues_c5f50255-1ea2-42bb-bb4b-cda73cf9b9fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_e055278c-4ae1-4d43-9795-2e9b869d702c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7fa0485a-94df-4d98-83aa-22984fcc0e67" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_e055278c-4ae1-4d43-9795-2e9b869d702c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockholdersEquityScheduleofStockholdersEquityDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#StockholdersEquityScheduleofStockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockholdersEquityScheduleofStockholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7a53bf4c-e356-44ae-a55d-2666b638020a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_095fb770-094f-4eb1-a93e-b633fd32fc5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7a53bf4c-e356-44ae-a55d-2666b638020a" xlink:to="loc_us-gaap_StatementTable_095fb770-094f-4eb1-a93e-b633fd32fc5d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_7e9957ba-1c97-4d07-bf9a-3b89b3625273" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_095fb770-094f-4eb1-a93e-b633fd32fc5d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_7e9957ba-1c97-4d07-bf9a-3b89b3625273" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_7e9957ba-1c97-4d07-bf9a-3b89b3625273_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7e9957ba-1c97-4d07-bf9a-3b89b3625273" xlink:to="loc_us-gaap_EquityComponentDomain_7e9957ba-1c97-4d07-bf9a-3b89b3625273_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_07bf8c42-e3c6-4dd7-b7ab-4612ace9e344" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7e9957ba-1c97-4d07-bf9a-3b89b3625273" xlink:to="loc_us-gaap_EquityComponentDomain_07bf8c42-e3c6-4dd7-b7ab-4612ace9e344" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_6b86cb28-3dee-4e3e-a79e-f6d8bd0b8e7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_07bf8c42-e3c6-4dd7-b7ab-4612ace9e344" xlink:to="loc_us-gaap_CommonStockMember_6b86cb28-3dee-4e3e-a79e-f6d8bd0b8e7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_eb3fb038-a101-495c-b206-641199c6e337" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_07bf8c42-e3c6-4dd7-b7ab-4612ace9e344" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_eb3fb038-a101-495c-b206-641199c6e337" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_da26fe3a-76c7-4409-ad05-c03ec384b502" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_07bf8c42-e3c6-4dd7-b7ab-4612ace9e344" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_da26fe3a-76c7-4409-ad05-c03ec384b502" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_927edc77-c0f4-4ad9-9560-c27e73ebdf47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_07bf8c42-e3c6-4dd7-b7ab-4612ace9e344" xlink:to="loc_us-gaap_RetainedEarningsMember_927edc77-c0f4-4ad9-9560-c27e73ebdf47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7a53bf4c-e356-44ae-a55d-2666b638020a" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_19ea77ac-5100-4075-85a6-91f7a9ab45e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_SharesOutstanding_19ea77ac-5100-4075-85a6-91f7a9ab45e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_911decd1-5f4d-4e23-a9b5-566815cf2e1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_StockholdersEquity_911decd1-5f4d-4e23-a9b5-566815cf2e1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_cb6da6c6-d0ac-4fdb-925d-9e56696cbbf6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_cb6da6c6-d0ac-4fdb-925d-9e56696cbbf6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_6fe146a8-6307-41c1-8edb-d0dd0efd27ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_6fe146a8-6307-41c1-8edb-d0dd0efd27ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_0ae016ad-5402-4e0e-8eee-e0c91ada8f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_0ae016ad-5402-4e0e-8eee-e0c91ada8f2d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_8e0ca0b5-b6e5-40ec-86ee-c4e493e97171" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_8e0ca0b5-b6e5-40ec-86ee-c4e493e97171" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_c7dce070-3eb1-4af4-8107-7a5580e496f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_c7dce070-3eb1-4af4-8107-7a5580e496f7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_b3942cff-5f65-494b-9d43-6e5d83a589c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_486b8e46-52ba-42ed-83d4-e287ed5ce939" xlink:to="loc_us-gaap_NetIncomeLoss_b3942cff-5f65-494b-9d43-6e5d83a589c8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_d5a40bc1-c1ba-43e0-b380-aa9b462b6b52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_bdbe005c-fb5e-4f01-8d1f-400907929d23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockBasedCompensationStockOptionsDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#StockBasedCompensationStockOptionsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockBasedCompensationStockOptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d6386da6-a807-4971-b190-a6af83990408" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d6386da6-a807-4971-b190-a6af83990408" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_6b9284ab-4929-4907-8c72-9848da91759b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d6386da6-a807-4971-b190-a6af83990408" xlink:to="loc_us-gaap_AwardTypeAxis_6b9284ab-4929-4907-8c72-9848da91759b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6b9284ab-4929-4907-8c72-9848da91759b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6b9284ab-4929-4907-8c72-9848da91759b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6b9284ab-4929-4907-8c72-9848da91759b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3156c6bb-dcf7-4738-9cd7-7e62e3473635" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6b9284ab-4929-4907-8c72-9848da91759b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3156c6bb-dcf7-4738-9cd7-7e62e3473635" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_33e167db-12ca-4a3d-92e6-cefd02b1c86a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3156c6bb-dcf7-4738-9cd7-7e62e3473635" xlink:to="loc_us-gaap_EmployeeStockOptionMember_33e167db-12ca-4a3d-92e6-cefd02b1c86a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_fc46076c-8837-4338-84a0-9c31dcf58fa7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_fc46076c-8837-4338-84a0-9c31dcf58fa7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_537cdd90-a15e-4b12-8de8-f1187b03af0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_fc46076c-8837-4338-84a0-9c31dcf58fa7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_537cdd90-a15e-4b12-8de8-f1187b03af0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_f4968dc4-a57d-4271-a389-c5302aecb9ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_fc46076c-8837-4338-84a0-9c31dcf58fa7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_f4968dc4-a57d-4271-a389-c5302aecb9ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_0ccb333d-c6ca-4f72-8336-904b2d171b9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_fc46076c-8837-4338-84a0-9c31dcf58fa7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_0ccb333d-c6ca-4f72-8336-904b2d171b9a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_95d17c5d-7ae2-412c-a4fb-d0873267b723" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_fc46076c-8837-4338-84a0-9c31dcf58fa7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_95d17c5d-7ae2-412c-a4fb-d0873267b723" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_c1ed456b-a2ca-4dc9-acd5-a8761ade6ce0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_423c8741-6300-4ddb-8916-2ae0e076fef9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_423c8741-6300-4ddb-8916-2ae0e076fef9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_d5f5b0c5-4f6a-4d81-9488-ff737bc969d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_d5f5b0c5-4f6a-4d81-9488-ff737bc969d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4755fa6d-608c-4840-9b8e-69ca160246bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4755fa6d-608c-4840-9b8e-69ca160246bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_a2cd9758-00a3-4edf-bbb1-0b5f5b806672" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4755fa6d-608c-4840-9b8e-69ca160246bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_a2cd9758-00a3-4edf-bbb1-0b5f5b806672" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_77c3b0c9-e610-4e7b-8eaf-a4ce67e4e821" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4755fa6d-608c-4840-9b8e-69ca160246bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_77c3b0c9-e610-4e7b-8eaf-a4ce67e4e821" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_4b1eaaf3-4714-483f-9ce5-54770e311c3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4755fa6d-608c-4840-9b8e-69ca160246bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_4b1eaaf3-4714-483f-9ce5-54770e311c3b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_0faba594-acc3-4d20-b968-c4e47c70a1ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4755fa6d-608c-4840-9b8e-69ca160246bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_0faba594-acc3-4d20-b968-c4e47c70a1ad" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_ed5af25b-3b22-4cb2-9106-d971aa2c4730" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_058e7900-fe69-4acf-9693-c9f4c0744f2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_058e7900-fe69-4acf-9693-c9f4c0744f2b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_daf53b13-1ce8-4b59-a57d-9fbd9606b314" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_daf53b13-1ce8-4b59-a57d-9fbd9606b314" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_b7d883a0-6ef7-4942-a0a9-a4b5fdc76077" xlink:href="qtrx-20250630.xsd#qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_b7d883a0-6ef7-4942-a0a9-a4b5fdc76077" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_34d2a6b7-e6da-4220-94d8-b524b3abe532" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_b7d883a0-6ef7-4942-a0a9-a4b5fdc76077" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_34d2a6b7-e6da-4220-94d8-b524b3abe532" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_81c5100d-96cd-45dd-994d-a8fdd5963b34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_b7d883a0-6ef7-4942-a0a9-a4b5fdc76077" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_81c5100d-96cd-45dd-994d-a8fdd5963b34" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_fe40c62b-c419-41d5-a1b7-a55d84fae1b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_b7d883a0-6ef7-4942-a0a9-a4b5fdc76077" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_fe40c62b-c419-41d5-a1b7-a55d84fae1b5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40895fde-d0bf-4fd7-9520-63eef1182355" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e34cdb53-3d88-414c-bc8a-ef9255cfecce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40895fde-d0bf-4fd7-9520-63eef1182355" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_f6ed0b50-befe-4049-9ca0-d31670301c56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40895fde-d0bf-4fd7-9520-63eef1182355" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_f6ed0b50-befe-4049-9ca0-d31670301c56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_818e0313-22e4-4948-b7f0-8bd6504ef495" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40895fde-d0bf-4fd7-9520-63eef1182355" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_818e0313-22e4-4948-b7f0-8bd6504ef495" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_a5195252-1565-4e41-b0a2-b101b6faea7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40895fde-d0bf-4fd7-9520-63eef1182355" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_a5195252-1565-4e41-b0a2-b101b6faea7a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockBasedCompensationRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#StockBasedCompensationRestrictedStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockBasedCompensationRestrictedStockUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_50889508-ab2b-4017-a923-3a6b14b3bb1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_11c0e9b6-aa3b-4422-b2ba-b61ddaebfacb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_50889508-ab2b-4017-a923-3a6b14b3bb1d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_11c0e9b6-aa3b-4422-b2ba-b61ddaebfacb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d8df4e4c-2324-404e-8639-f7318a2b9787" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_11c0e9b6-aa3b-4422-b2ba-b61ddaebfacb" xlink:to="loc_us-gaap_AwardTypeAxis_d8df4e4c-2324-404e-8639-f7318a2b9787" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d8df4e4c-2324-404e-8639-f7318a2b9787_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d8df4e4c-2324-404e-8639-f7318a2b9787" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d8df4e4c-2324-404e-8639-f7318a2b9787_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0c904091-9eb5-4069-90fe-59a36313a88c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d8df4e4c-2324-404e-8639-f7318a2b9787" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0c904091-9eb5-4069-90fe-59a36313a88c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_c8edea54-544a-48e2-a4e6-68ef8087fba1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0c904091-9eb5-4069-90fe-59a36313a88c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_c8edea54-544a-48e2-a4e6-68ef8087fba1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_0eb19dc2-561a-4458-88de-e06da813c01e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_50889508-ab2b-4017-a923-3a6b14b3bb1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_0eb19dc2-561a-4458-88de-e06da813c01e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_8aa1076a-76ef-4638-a949-098deb539061" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_0eb19dc2-561a-4458-88de-e06da813c01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_8aa1076a-76ef-4638-a949-098deb539061" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_057e5636-0b8a-4005-914a-373ce0ada0d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_0eb19dc2-561a-4458-88de-e06da813c01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_057e5636-0b8a-4005-914a-373ce0ada0d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_9a543b4e-81b8-4cb9-b6be-d594a37e5598" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_0eb19dc2-561a-4458-88de-e06da813c01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_9a543b4e-81b8-4cb9-b6be-d594a37e5598" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_c93e14e4-fff9-4220-8744-638dea743c9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_0eb19dc2-561a-4458-88de-e06da813c01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_c93e14e4-fff9-4220-8744-638dea743c9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_0acddf3b-2c03-4a86-978b-08b6e1b27651" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d9aed644-4ffc-44e9-a7f0-e17bc9c6dc0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_50889508-ab2b-4017-a923-3a6b14b3bb1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d9aed644-4ffc-44e9-a7f0-e17bc9c6dc0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_aab9a2ef-1d22-4328-9620-2979817b8bd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d9aed644-4ffc-44e9-a7f0-e17bc9c6dc0f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_aab9a2ef-1d22-4328-9620-2979817b8bd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0c261bad-a1ab-4492-bbe8-119a5ef3595c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d9aed644-4ffc-44e9-a7f0-e17bc9c6dc0f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0c261bad-a1ab-4492-bbe8-119a5ef3595c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_4535ea2f-1dd6-4746-ae4b-a08226a51aee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d9aed644-4ffc-44e9-a7f0-e17bc9c6dc0f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_4535ea2f-1dd6-4746-ae4b-a08226a51aee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_3fb78698-3340-42db-95f6-a41d49394705" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d9aed644-4ffc-44e9-a7f0-e17bc9c6dc0f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_3fb78698-3340-42db-95f6-a41d49394705" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_be3434be-0861-4875-b830-f3cce4fead35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockBasedCompensationEmployeeStockPurchasePlanESPPDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#StockBasedCompensationEmployeeStockPurchasePlanESPPDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockBasedCompensationEmployeeStockPurchasePlanESPPDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1666de79-7e48-4cd1-861b-2f24b061cec8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c67126bd-02cf-415c-89a9-447ef64d37ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1666de79-7e48-4cd1-861b-2f24b061cec8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c67126bd-02cf-415c-89a9-447ef64d37ca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_e840c652-3786-4fad-a140-df21a3389d26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c67126bd-02cf-415c-89a9-447ef64d37ca" xlink:to="loc_us-gaap_PlanNameAxis_e840c652-3786-4fad-a140-df21a3389d26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_e840c652-3786-4fad-a140-df21a3389d26_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_e840c652-3786-4fad-a140-df21a3389d26" xlink:to="loc_us-gaap_PlanNameDomain_e840c652-3786-4fad-a140-df21a3389d26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_51674726-9bac-43d2-bb91-cfc57020d58d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_e840c652-3786-4fad-a140-df21a3389d26" xlink:to="loc_us-gaap_PlanNameDomain_51674726-9bac-43d2-bb91-cfc57020d58d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_A2017ESPPMember_5a60cd1c-5863-48f5-a546-822321316117" xlink:href="qtrx-20250630.xsd#qtrx_A2017ESPPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_51674726-9bac-43d2-bb91-cfc57020d58d" xlink:to="loc_qtrx_A2017ESPPMember_5a60cd1c-5863-48f5-a546-822321316117" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_9225f33c-8bd8-423a-bcc2-5185db20e958" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1666de79-7e48-4cd1-861b-2f24b061cec8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_9225f33c-8bd8-423a-bcc2-5185db20e958" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockBasedCompensationShareBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#StockBasedCompensationShareBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockBasedCompensationShareBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5c2463cb-9be7-4a77-ac51-cc3492947670" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_948053cc-53f1-4032-91ef-6911ae573e12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5c2463cb-9be7-4a77-ac51-cc3492947670" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_948053cc-53f1-4032-91ef-6911ae573e12" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d48f6c7d-2734-4e4a-82c9-9fe0ce07f239" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_948053cc-53f1-4032-91ef-6911ae573e12" xlink:to="loc_us-gaap_AwardTypeAxis_d48f6c7d-2734-4e4a-82c9-9fe0ce07f239" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d48f6c7d-2734-4e4a-82c9-9fe0ce07f239_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d48f6c7d-2734-4e4a-82c9-9fe0ce07f239" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d48f6c7d-2734-4e4a-82c9-9fe0ce07f239_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df8f4090-15b0-4de8-abfe-6c55a42df686" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d48f6c7d-2734-4e4a-82c9-9fe0ce07f239" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df8f4090-15b0-4de8-abfe-6c55a42df686" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_RestrictedStockUnitsAndStockOptionsMember_81acb1cd-0def-479f-9f7d-527259eac0c1" xlink:href="qtrx-20250630.xsd#qtrx_RestrictedStockUnitsAndStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df8f4090-15b0-4de8-abfe-6c55a42df686" xlink:to="loc_qtrx_RestrictedStockUnitsAndStockOptionsMember_81acb1cd-0def-479f-9f7d-527259eac0c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_a6f2463d-f89c-4f9f-b0f8-f3aa704be914" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_948053cc-53f1-4032-91ef-6911ae573e12" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_a6f2463d-f89c-4f9f-b0f8-f3aa704be914" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a6f2463d-f89c-4f9f-b0f8-f3aa704be914_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_a6f2463d-f89c-4f9f-b0f8-f3aa704be914" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a6f2463d-f89c-4f9f-b0f8-f3aa704be914_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d7753238-7f08-4f42-ba90-1c0072d209ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_a6f2463d-f89c-4f9f-b0f8-f3aa704be914" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d7753238-7f08-4f42-ba90-1c0072d209ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_CostOfProductRevenueMember_ca3e611d-47a6-482a-a432-16638de84e56" xlink:href="qtrx-20250630.xsd#qtrx_CostOfProductRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d7753238-7f08-4f42-ba90-1c0072d209ff" xlink:to="loc_qtrx_CostOfProductRevenueMember_ca3e611d-47a6-482a-a432-16638de84e56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceAndOtherRevenueMember_073fefca-137e-401a-a28c-79ef6e23ee78" xlink:href="qtrx-20250630.xsd#qtrx_ServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d7753238-7f08-4f42-ba90-1c0072d209ff" xlink:to="loc_qtrx_ServiceAndOtherRevenueMember_073fefca-137e-401a-a28c-79ef6e23ee78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_1f8e0b91-4328-4e63-bc2b-9af76846bf76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d7753238-7f08-4f42-ba90-1c0072d209ff" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_1f8e0b91-4328-4e63-bc2b-9af76846bf76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_d4888515-1b99-4c06-8696-9a47c8ca892b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d7753238-7f08-4f42-ba90-1c0072d209ff" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_d4888515-1b99-4c06-8696-9a47c8ca892b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_a6e824f9-7a71-47db-9b15-3e863727af33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5c2463cb-9be7-4a77-ac51-cc3492947670" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_a6e824f9-7a71-47db-9b15-3e863727af33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_33174ddb-ed9e-4074-ae3d-a8d321540dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5c2463cb-9be7-4a77-ac51-cc3492947670" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_33174ddb-ed9e-4074-ae3d-a8d321540dc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_354ddaad-c68b-474d-9f02-4f18f3f350f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5c2463cb-9be7-4a77-ac51-cc3492947670" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_354ddaad-c68b-474d-9f02-4f18f3f350f7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/NetLossPerShareCommonShareEquivalentsExcludedfromDilutedNetLossPerShareDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#NetLossPerShareCommonShareEquivalentsExcludedfromDilutedNetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/NetLossPerShareCommonShareEquivalentsExcludedfromDilutedNetLossPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_a9d93f53-b87d-421c-94b3-4383d13d936e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_3cf52164-69b4-4935-8b64-ed4283883cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_a9d93f53-b87d-421c-94b3-4383d13d936e" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_3cf52164-69b4-4935-8b64-ed4283883cfc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8237d801-77e3-4661-9a5a-0631b249f8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_3cf52164-69b4-4935-8b64-ed4283883cfc" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8237d801-77e3-4661-9a5a-0631b249f8e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8237d801-77e3-4661-9a5a-0631b249f8e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8237d801-77e3-4661-9a5a-0631b249f8e4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8237d801-77e3-4661-9a5a-0631b249f8e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5550607f-5e78-4e16-bda5-c8a451496612" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8237d801-77e3-4661-9a5a-0631b249f8e4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5550607f-5e78-4e16-bda5-c8a451496612" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_e339e90d-ee4c-4183-b326-22d282fbb41d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5550607f-5e78-4e16-bda5-c8a451496612" xlink:to="loc_us-gaap_EmployeeStockOptionMember_e339e90d-ee4c-4183-b326-22d282fbb41d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_234e8429-b753-4c75-8ba3-9c552e8a68f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5550607f-5e78-4e16-bda5-c8a451496612" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_234e8429-b753-4c75-8ba3-9c552e8a68f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EstimatedEsppPurchasesMember_ad7a9df5-53a3-40c1-8716-ab2ca9a53545" xlink:href="qtrx-20250630.xsd#qtrx_EstimatedEsppPurchasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5550607f-5e78-4e16-bda5-c8a451496612" xlink:to="loc_qtrx_EstimatedEsppPurchasesMember_ad7a9df5-53a3-40c1-8716-ab2ca9a53545" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_55892944-7f56-494e-9e2c-1005233d1c63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_a9d93f53-b87d-421c-94b3-4383d13d936e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_55892944-7f56-494e-9e2c-1005233d1c63" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_98d9a191-9231-476d-81f6-f7673a0dcb41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:to="loc_us-gaap_OtherCommitmentsTable_98d9a191-9231-476d-81f6-f7673a0dcb41" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_fb1f9d75-2487-4d03-b625-62cdb2d5b84f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_98d9a191-9231-476d-81f6-f7673a0dcb41" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_fb1f9d75-2487-4d03-b625-62cdb2d5b84f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_fb1f9d75-2487-4d03-b625-62cdb2d5b84f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_fb1f9d75-2487-4d03-b625-62cdb2d5b84f" xlink:to="loc_us-gaap_RelatedPartyDomain_fb1f9d75-2487-4d03-b625-62cdb2d5b84f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_1134bfb2-2790-44de-b671-99287b3d7e72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_fb1f9d75-2487-4d03-b625-62cdb2d5b84f" xlink:to="loc_us-gaap_RelatedPartyDomain_1134bfb2-2790-44de-b671-99287b3d7e72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_HarvardUniversityMember_fb0bfedf-4fa3-4337-9b02-3a3028ba6228" xlink:href="qtrx-20250630.xsd#qtrx_HarvardUniversityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_1134bfb2-2790-44de-b671-99287b3d7e72" xlink:to="loc_qtrx_HarvardUniversityMember_fb0bfedf-4fa3-4337-9b02-3a3028ba6228" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_TuftsMember_eacdcb23-e75d-4bfe-8200-85197a65c115" xlink:href="qtrx-20250630.xsd#qtrx_TuftsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_1134bfb2-2790-44de-b671-99287b3d7e72" xlink:to="loc_qtrx_TuftsMember_eacdcb23-e75d-4bfe-8200-85197a65c115" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_a206d4e8-d6ea-4bac-9c1a-9098d412f320" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_98d9a191-9231-476d-81f6-f7673a0dcb41" xlink:to="loc_us-gaap_TypeOfArrangementAxis_a206d4e8-d6ea-4bac-9c1a-9098d412f320" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_a206d4e8-d6ea-4bac-9c1a-9098d412f320_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_a206d4e8-d6ea-4bac-9c1a-9098d412f320" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_a206d4e8-d6ea-4bac-9c1a-9098d412f320_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_e7625b11-ce3a-4452-a717-0392feb92de9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_a206d4e8-d6ea-4bac-9c1a-9098d412f320" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_e7625b11-ce3a-4452-a717-0392feb92de9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_LicenseAgreementsMember_b1c86b51-a0f4-41b6-9728-24a381b54c47" xlink:href="qtrx-20250630.xsd#qtrx_LicenseAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_e7625b11-ce3a-4452-a717-0392feb92de9" xlink:to="loc_qtrx_LicenseAgreementsMember_b1c86b51-a0f4-41b6-9728-24a381b54c47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_SupplyAgreementNoticePeriodForTermination_1d6a3474-2261-4794-a21c-6c4d51386abf" xlink:href="qtrx-20250630.xsd#qtrx_SupplyAgreementNoticePeriodForTermination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:to="loc_qtrx_SupplyAgreementNoticePeriodForTermination_1d6a3474-2261-4794-a21c-6c4d51386abf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligation_bc3e0959-a533-4d84-b895-a1db7167fa2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:to="loc_us-gaap_PurchaseObligation_bc3e0959-a533-4d84-b895-a1db7167fa2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentDueInNextTwelveMonths_610ba4e1-2054-4ea8-908e-8aeb2095bd53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:to="loc_us-gaap_OtherCommitmentDueInNextTwelveMonths_610ba4e1-2054-4ea8-908e-8aeb2095bd53" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_UpfrontFee_93609eac-3d41-4b10-8239-310db37b1fba" xlink:href="qtrx-20250630.xsd#qtrx_UpfrontFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:to="loc_qtrx_UpfrontFee_93609eac-3d41-4b10-8239-310db37b1fba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyExpense_362b5624-96f9-47c0-addf-ef971253d5ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RoyaltyExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_58b83d87-83f9-4e56-b446-a9f39ea9596d" xlink:to="loc_us-gaap_RoyaltyExpense_362b5624-96f9-47c0-addf-ef971253d5ef" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_8906dd53-9b41-41ec-abe1-e176b16e3aab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_8906dd53-9b41-41ec-abe1-e176b16e3aab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2392981a-2d0f-4a36-a2c2-c835f8b18bb5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_8906dd53-9b41-41ec-abe1-e176b16e3aab" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2392981a-2d0f-4a36-a2c2-c835f8b18bb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_2392981a-2d0f-4a36-a2c2-c835f8b18bb5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2392981a-2d0f-4a36-a2c2-c835f8b18bb5" xlink:to="loc_us-gaap_RelatedPartyDomain_2392981a-2d0f-4a36-a2c2-c835f8b18bb5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_2a66303e-aab8-4fe6-97f6-e4f283c8eb07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2392981a-2d0f-4a36-a2c2-c835f8b18bb5" xlink:to="loc_us-gaap_RelatedPartyDomain_2a66303e-aab8-4fe6-97f6-e4f283c8eb07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_94f4c396-549f-4855-81cb-ca91b357c44c" xlink:href="qtrx-20250630.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_2a66303e-aab8-4fe6-97f6-e4f283c8eb07" xlink:to="loc_qtrx_EmissionInc.Member_94f4c396-549f-4855-81cb-ca91b357c44c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_HarvardUniversityMember_00523d01-41cf-4351-a696-e6ad04f4af98" xlink:href="qtrx-20250630.xsd#qtrx_HarvardUniversityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_2a66303e-aab8-4fe6-97f6-e4f283c8eb07" xlink:to="loc_qtrx_HarvardUniversityMember_00523d01-41cf-4351-a696-e6ad04f4af98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_TuftsMember_6f2140c2-1a57-4245-b8e2-5e43ab71ad72" xlink:href="qtrx-20250630.xsd#qtrx_TuftsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_2a66303e-aab8-4fe6-97f6-e4f283c8eb07" xlink:to="loc_qtrx_TuftsMember_6f2140c2-1a57-4245-b8e2-5e43ab71ad72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_e217a0d9-01b8-4986-b836-bb8f762b14fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:to="loc_us-gaap_OperatingExpenses_e217a0d9-01b8-4986-b836-bb8f762b14fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_1b689e62-34f9-483d-9490-be9c7066eeab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:to="loc_us-gaap_Revenues_1b689e62-34f9-483d-9490-be9c7066eeab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_afebc46d-388f-43a1-b3c1-76ee67159734" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:to="loc_us-gaap_CostOfRevenue_afebc46d-388f-43a1-b3c1-76ee67159734" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_ba00a8d0-b544-4e10-98c1-ec9a7e1208a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:to="loc_us-gaap_AccountsPayableCurrent_ba00a8d0-b544-4e10-98c1-ec9a7e1208a2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_b9e6d5e1-0ec9-495a-8586-0e4c6f272924" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_014d6e15-b59c-477a-b599-26637c02ff50" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_b9e6d5e1-0ec9-495a-8586-0e4c6f272924" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/VariableInterestEntitiesDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#VariableInterestEntitiesDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/VariableInterestEntitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_31e43a61-5cfd-4381-aacb-fbbbbf84e214" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dc1549e0-d300-4d2f-a06b-0badf842a208" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_31e43a61-5cfd-4381-aacb-fbbbbf84e214" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dc1549e0-d300-4d2f-a06b-0badf842a208" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_77636fa5-255b-4168-b37e-449f63f1b8ac" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dc1549e0-d300-4d2f-a06b-0badf842a208" xlink:to="loc_srt_ConsolidatedEntitiesAxis_77636fa5-255b-4168-b37e-449f63f1b8ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_77636fa5-255b-4168-b37e-449f63f1b8ac_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_77636fa5-255b-4168-b37e-449f63f1b8ac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_77636fa5-255b-4168-b37e-449f63f1b8ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_46dd876d-1313-4fa5-9d65-e36bac844686" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_77636fa5-255b-4168-b37e-449f63f1b8ac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_46dd876d-1313-4fa5-9d65-e36bac844686" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_bedb340c-5a76-4e3f-bf2f-3520dc74bd5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_46dd876d-1313-4fa5-9d65-e36bac844686" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_bedb340c-5a76-4e3f-bf2f-3520dc74bd5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_b113c097-8fb5-440e-92ad-027ae22240c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_31e43a61-5cfd-4381-aacb-fbbbbf84e214" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_b113c097-8fb5-440e-92ad-027ae22240c2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/SegmentReportingScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#SegmentReportingScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/SegmentReportingScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingAssetReconcilingItemLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_dffdd6d7-fa4f-4250-a403-bf02655cf41d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:to="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_dffdd6d7-fa4f-4250-a403-bf02655cf41d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_5458f4d8-9112-4b7b-b887-8c6f030cf889" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_dffdd6d7-fa4f-4250-a403-bf02655cf41d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_5458f4d8-9112-4b7b-b887-8c6f030cf889" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_5458f4d8-9112-4b7b-b887-8c6f030cf889_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5458f4d8-9112-4b7b-b887-8c6f030cf889" xlink:to="loc_us-gaap_SegmentDomain_5458f4d8-9112-4b7b-b887-8c6f030cf889_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_f4b6043d-3610-43a8-9a8b-4221bb658f51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5458f4d8-9112-4b7b-b887-8c6f030cf889" xlink:to="loc_us-gaap_SegmentDomain_f4b6043d-3610-43a8-9a8b-4221bb658f51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ReportableSegmentMember_b6cbfa93-bdaa-492f-ba7b-20df2aa86cc8" xlink:href="qtrx-20250630.xsd#qtrx_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f4b6043d-3610-43a8-9a8b-4221bb658f51" xlink:to="loc_qtrx_ReportableSegmentMember_b6cbfa93-bdaa-492f-ba7b-20df2aa86cc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_9400b8bf-7da5-44df-9c98-e80cc4d6ceb0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_dffdd6d7-fa4f-4250-a403-bf02655cf41d" xlink:to="loc_srt_ProductOrServiceAxis_9400b8bf-7da5-44df-9c98-e80cc4d6ceb0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_9400b8bf-7da5-44df-9c98-e80cc4d6ceb0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_9400b8bf-7da5-44df-9c98-e80cc4d6ceb0" xlink:to="loc_srt_ProductsAndServicesDomain_9400b8bf-7da5-44df-9c98-e80cc4d6ceb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_1331206d-fab2-4c98-be2d-2d2206190422" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_9400b8bf-7da5-44df-9c98-e80cc4d6ceb0" xlink:to="loc_srt_ProductsAndServicesDomain_1331206d-fab2-4c98-be2d-2d2206190422" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantMember_6309296a-4b4d-4b7e-ada5-a18750a2819d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1331206d-fab2-4c98-be2d-2d2206190422" xlink:to="loc_us-gaap_GrantMember_6309296a-4b4d-4b7e-ada5-a18750a2819d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9ff1be75-eccf-4f10-a99f-9dd8f32205b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9ff1be75-eccf-4f10-a99f-9dd8f32205b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_806348cf-f3ec-4a61-b0d2-15b1e8d5fd1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_806348cf-f3ec-4a61-b0d2-15b1e8d5fd1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_f8ccb0ea-2df4-4a8c-a4f4-7f6fba6ef8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_f8ccb0ea-2df4-4a8c-a4f4-7f6fba6ef8ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_0746c43a-aa14-4aaf-a896-935e8ed17b20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_0746c43a-aa14-4aaf-a896-935e8ed17b20" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_1aa6110c-d316-4e87-aff6-d35e77f3c128" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_03112124-7a56-4e91-97eb-f09a5cd4de44" xlink:to="loc_us-gaap_NetIncomeLoss_1aa6110c-d316-4e87-aff6-d35e77f3c128" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="qtrx-20250630.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_c39e7f59-ce3c-4e17-9b04-0976935dc319" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_us-gaap_SubsequentEventTable_c39e7f59-ce3c-4e17-9b04-0976935dc319" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_5b2ac642-1c96-45d0-8576-fe50d386ab2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_c39e7f59-ce3c-4e17-9b04-0976935dc319" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_5b2ac642-1c96-45d0-8576-fe50d386ab2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5b2ac642-1c96-45d0-8576-fe50d386ab2a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5b2ac642-1c96-45d0-8576-fe50d386ab2a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5b2ac642-1c96-45d0-8576-fe50d386ab2a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a6dc3ccc-2a14-40f9-8e6f-8186d7d1a1e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5b2ac642-1c96-45d0-8576-fe50d386ab2a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a6dc3ccc-2a14-40f9-8e6f-8186d7d1a1e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_11cab2ad-48f3-4dd7-9337-2471112d6d9a" xlink:href="qtrx-20250630.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a6dc3ccc-2a14-40f9-8e6f-8186d7d1a1e6" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_11cab2ad-48f3-4dd7-9337-2471112d6d9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_7e500f20-305a-42da-abf0-ddb847f4d251" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_c39e7f59-ce3c-4e17-9b04-0976935dc319" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_7e500f20-305a-42da-abf0-ddb847f4d251" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_7e500f20-305a-42da-abf0-ddb847f4d251_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_7e500f20-305a-42da-abf0-ddb847f4d251" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_7e500f20-305a-42da-abf0-ddb847f4d251_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_f90d8e86-ace0-433a-9960-347ac6d8e742" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_7e500f20-305a-42da-abf0-ddb847f4d251" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_f90d8e86-ace0-433a-9960-347ac6d8e742" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_91f69615-3f5b-4c6a-b59e-cc41d4853c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_f90d8e86-ace0-433a-9960-347ac6d8e742" xlink:to="loc_us-gaap_SubsequentEventMember_91f69615-3f5b-4c6a-b59e-cc41d4853c0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_ee86f86e-b338-41c0-a4e4-546fc198c6c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_ee86f86e-b338-41c0-a4e4-546fc198c6c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessAcquisitionEquityConversionRatio_b382799f-5a6f-4eb9-b83b-205a9ba23b0b" xlink:href="qtrx-20250630.xsd#qtrx_BusinessAcquisitionEquityConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_qtrx_BusinessAcquisitionEquityConversionRatio_b382799f-5a6f-4eb9-b83b-205a9ba23b0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessAcquisitionConsiderationTransferredCashPaidPerShare_9409facb-0368-4e88-bdf4-4f8daa7fd2fb" xlink:href="qtrx-20250630.xsd#qtrx_BusinessAcquisitionConsiderationTransferredCashPaidPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_qtrx_BusinessAcquisitionConsiderationTransferredCashPaidPerShare_9409facb-0368-4e88-bdf4-4f8daa7fd2fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_fb02dfd2-dc38-44c8-8801-b418fabb6713" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_fb02dfd2-dc38-44c8-8801-b418fabb6713" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_4f8345aa-73dd-430e-9389-1dfa5f936d46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_4f8345aa-73dd-430e-9389-1dfa5f936d46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredLiabilityPaid_df172789-1aa8-49b0-a3ec-5095f075e7a3" xlink:href="qtrx-20250630.xsd#qtrx_BusinessCombinationConsiderationTransferredLiabilityPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredLiabilityPaid_df172789-1aa8-49b0-a3ec-5095f075e7a3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredSettlementOfPrincipalOutstanding_5ad20688-134c-476e-8d4a-aa5d9f9c22fb" xlink:href="qtrx-20250630.xsd#qtrx_BusinessCombinationConsiderationTransferredSettlementOfPrincipalOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredSettlementOfPrincipalOutstanding_5ad20688-134c-476e-8d4a-aa5d9f9c22fb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredSettlementOfEarlyTerminationLegalAndPrepaymentFees_32b2d496-13d1-43b4-83b9-5aaed0e1b73a" xlink:href="qtrx-20250630.xsd#qtrx_BusinessCombinationConsiderationTransferredSettlementOfEarlyTerminationLegalAndPrepaymentFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredSettlementOfEarlyTerminationLegalAndPrepaymentFees_32b2d496-13d1-43b4-83b9-5aaed0e1b73a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_549ed3d5-6928-4d10-ae94-578ea96879d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e45ae8c6-970a-4869-b16a-5134d713ccd4" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_549ed3d5-6928-4d10-ae94-578ea96879d8" xlink:type="arc" order="8"/>
  </link:definitionLink>
</link:linkbase>
