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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019d0647-9da8-79bf-a50b-90c628115914,g:957eeec0-b2e6-4f7c-a05d-1b7dac52a708-->
<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-20260331.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_019d0647-9f08-7125-963d-480083ef8350" 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_019d0647-9f08-7434-836b-372cfc34e351" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_StatementTable_019d0647-9f08-7434-836b-372cfc34e351" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d0647-9f08-7747-8e51-12a842bb1292" 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_019d0647-9f08-7434-836b-372cfc34e351" xlink:to="loc_srt_ProductOrServiceAxis_019d0647-9f08-7747-8e51-12a842bb1292" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d0647-9f08-7747-8e51-12a842bb1292_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_019d0647-9f08-7747-8e51-12a842bb1292" xlink:to="loc_srt_ProductsAndServicesDomain_019d0647-9f08-7747-8e51-12a842bb1292_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d0647-9f08-7701-8bc9-2fe84a887b16" 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_019d0647-9f08-7747-8e51-12a842bb1292" xlink:to="loc_srt_ProductsAndServicesDomain_019d0647-9f08-7701-8bc9-2fe84a887b16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019d0647-9f08-722c-9f91-efee8c99056a" 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_019d0647-9f08-7701-8bc9-2fe84a887b16" xlink:to="loc_us-gaap_ProductMember_019d0647-9f08-722c-9f91-efee8c99056a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7ed2-a465-14b58190c90b" xlink:href="qtrx-20260331.xsd#qtrx_ServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d0647-9f08-7701-8bc9-2fe84a887b16" xlink:to="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7ed2-a465-14b58190c90b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseAndServiceMember_019d0647-9f08-7169-a194-45f60065b6f2" 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_019d0647-9f08-7701-8bc9-2fe84a887b16" xlink:to="loc_us-gaap_LicenseAndServiceMember_019d0647-9f08-7169-a194-45f60065b6f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019d0647-9f08-7fc4-807b-d04e5204ca8a" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_RevenuesAbstract_019d0647-9f08-7fc4-807b-d04e5204ca8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019d0647-9f08-7bfd-a270-3225a60bf537" 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_019d0647-9f08-7fc4-807b-d04e5204ca8a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019d0647-9f08-7bfd-a270-3225a60bf537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_019d0647-9f08-7dce-b476-8ead31bc6479" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_019d0647-9f08-7dce-b476-8ead31bc6479" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019d0647-9f08-7d7f-a619-88f8669c12ca" 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_019d0647-9f08-7dce-b476-8ead31bc6479" xlink:to="loc_us-gaap_CostOfRevenue_019d0647-9f08-7d7f-a619-88f8669c12ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019d0647-9f08-76c8-b0de-f65c59d68cf6" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_GrossProfit_019d0647-9f08-76c8-b0de-f65c59d68cf6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019d0647-9f08-7147-b29d-be65650838a5" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019d0647-9f08-7147-b29d-be65650838a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019d0647-9f08-71be-bdc0-3ac983a4d77e" 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_019d0647-9f08-7147-b29d-be65650838a5" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019d0647-9f08-71be-bdc0-3ac983a4d77e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019db83c-ab42-7824-aba9-e186dbd9a446" 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_019d0647-9f08-7147-b29d-be65650838a5" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019db83c-ab42-7824-aba9-e186dbd9a446" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_019d0647-9f08-7c80-b2af-3b13d2ba72b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019d0647-9f08-7147-b29d-be65650838a5" xlink:to="loc_us-gaap_AssetImpairmentCharges_019d0647-9f08-7c80-b2af-3b13d2ba72b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_019d0647-9f08-7a5f-8f50-167c0c1ce23d" 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_019d0647-9f08-7147-b29d-be65650838a5" xlink:to="loc_us-gaap_OperatingExpenses_019d0647-9f08-7a5f-8f50-167c0c1ce23d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019d0647-9f08-7542-a2a9-543057436fa5" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_OperatingIncomeLoss_019d0647-9f08-7542-a2a9-543057436fa5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncomeAndExpensesAbstract_019d0647-9f08-794f-a424-9fea1a13b074" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_OtherIncomeAndExpensesAbstract_019d0647-9f08-794f-a424-9fea1a13b074" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019d0647-9f08-7e35-b40d-e08040b7b678" 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_019d0647-9f08-794f-a424-9fea1a13b074" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019d0647-9f08-7e35-b40d-e08040b7b678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_019d0647-9f08-76ad-b971-0803f88d3c65" 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_019d0647-9f08-794f-a424-9fea1a13b074" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_019d0647-9f08-76ad-b971-0803f88d3c65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019d0647-9f08-7f0d-8f87-cf4e6a4849f4" 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_019d0647-9f08-794f-a424-9fea1a13b074" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019d0647-9f08-7f0d-8f87-cf4e6a4849f4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019d0647-9f08-7d94-a03f-6b254656baf5" 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_019d0647-9f08-794f-a424-9fea1a13b074" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019d0647-9f08-7d94-a03f-6b254656baf5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019d0647-9f08-7f1f-8e21-1f4ace1800a0" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019d0647-9f08-7f1f-8e21-1f4ace1800a0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d0647-9f08-73fb-8083-52776e3914d7" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_NetIncomeLoss_019d0647-9f08-73fb-8083-52776e3914d7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019d0647-9f08-7982-b096-9c92b5d19ac2" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_EarningsPerShareBasic_019d0647-9f08-7982-b096-9c92b5d19ac2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019d0647-9f08-77e6-9fbc-d8baf9f24cea" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019d0647-9f08-77e6-9fbc-d8baf9f24cea" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019d0647-9f08-7b98-964d-7f338d8cd29e" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019d0647-9f08-7b98-964d-7f338d8cd29e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019d0647-9f08-7042-b52d-c8d9a2add1eb" 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_019d0647-9f08-7125-963d-480083ef8350" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019d0647-9f08-7042-b52d-c8d9a2add1eb" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/SignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#SignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/SignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_019df1f5-767b-72be-a086-efe0db86329e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019df1f5-767b-7413-9d67-7cb597241dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_019df1f5-767b-72be-a086-efe0db86329e" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019df1f5-767b-7413-9d67-7cb597241dc2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019df1f5-767b-7082-8b50-a84288403c45" 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_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019df1f5-767b-7413-9d67-7cb597241dc2" xlink:to="loc_srt_ProductOrServiceAxis_019df1f5-767b-7082-8b50-a84288403c45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019df1f5-767b-7082-8b50-a84288403c45_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_019df1f5-767b-7082-8b50-a84288403c45" xlink:to="loc_srt_ProductsAndServicesDomain_019df1f5-767b-7082-8b50-a84288403c45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019df1f5-767b-7ffe-a49d-1f0046deada4" 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_019df1f5-767b-7082-8b50-a84288403c45" xlink:to="loc_srt_ProductsAndServicesDomain_019df1f5-767b-7ffe-a49d-1f0046deada4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019df1f5-767b-7f3a-9763-5d172acd9a12" 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_019df1f5-767b-7ffe-a49d-1f0046deada4" xlink:to="loc_us-gaap_ProductMember_019df1f5-767b-7f3a-9763-5d172acd9a12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis_019df1f5-767b-726e-a241-825b2f60955c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019df1f5-767b-7413-9d67-7cb597241dc2" xlink:to="loc_us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis_019df1f5-767b-726e-a241-825b2f60955c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingPrincipleMember_019df1f5-767b-726e-a241-825b2f60955c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingPrincipleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis_019df1f5-767b-726e-a241-825b2f60955c" xlink:to="loc_us-gaap_ChangeInAccountingPrincipleMember_019df1f5-767b-726e-a241-825b2f60955c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingPrincipleMember_019df1f5-767b-7d00-8ee5-a2bab8e519e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingPrincipleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis_019df1f5-767b-726e-a241-825b2f60955c" xlink:to="loc_us-gaap_ChangeInAccountingPrincipleMember_019df1f5-767b-7d00-8ee5-a2bab8e519e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ReclassificationOfSellingGeneralAndAdministrativeToCostOfProductRevenueMember_019df1f5-767b-7b5d-9b87-0a033a2028ff" xlink:href="qtrx-20260331.xsd#qtrx_ReclassificationOfSellingGeneralAndAdministrativeToCostOfProductRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingPrincipleMember_019df1f5-767b-7d00-8ee5-a2bab8e519e5" xlink:to="loc_qtrx_ReclassificationOfSellingGeneralAndAdministrativeToCostOfProductRevenueMember_019df1f5-767b-7b5d-9b87-0a033a2028ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019df1f5-767b-7235-bfb9-dff5378c527e" 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_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_019df1f5-767b-72be-a086-efe0db86329e" xlink:to="loc_us-gaap_CostOfRevenue_019df1f5-767b-7235-bfb9-dff5378c527e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20260331.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_019d2879-f39c-71bb-8af3-e81b4ca58315" 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_019d0647-9f08-7f55-9a2e-91a0901c6a96" 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_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7f55-9a2e-91a0901c6a96" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d2879-f39c-7ebd-beb0-d27e623fc7df" 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_019d0647-9f08-7f55-9a2e-91a0901c6a96" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d2879-f39c-7ebd-beb0-d27e623fc7df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d2879-f39c-7ebd-beb0-d27e623fc7df_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_019d2879-f39c-7ebd-beb0-d27e623fc7df" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d2879-f39c-7ebd-beb0-d27e623fc7df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d2879-f39c-700e-b3fe-004defcb620f" 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_019d2879-f39c-7ebd-beb0-d27e623fc7df" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d2879-f39c-700e-b3fe-004defcb620f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019d287a-3298-74d8-8a41-338f3e71928d" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d2879-f39c-700e-b3fe-004defcb620f" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019d287a-3298-74d8-8a41-338f3e71928d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_019d2880-d76c-7501-a1e2-a3c14886a079" xlink:href="qtrx-20260331.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d2879-f39c-700e-b3fe-004defcb620f" xlink:to="loc_qtrx_EmissionInc.Member_019d2880-d76c-7501-a1e2-a3c14886a079" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d67b9-a12e-7dbe-8a75-2af959b3fdae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7f55-9a2e-91a0901c6a96" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d67b9-a12e-7dbe-8a75-2af959b3fdae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d67b9-a12e-7dbe-8a75-2af959b3fdae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d67b9-a12e-7dbe-8a75-2af959b3fdae" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d67b9-a12e-7dbe-8a75-2af959b3fdae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d67b9-a12e-7dec-b557-6c08d74b9854" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d67b9-a12e-7dbe-8a75-2af959b3fdae" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d67b9-a12e-7dec-b557-6c08d74b9854" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_019d67b9-a12e-728c-9dda-516ff3961159" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d67b9-a12e-7dec-b557-6c08d74b9854" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_019d67b9-a12e-728c-9dda-516ff3961159" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_019d2880-d76c-7799-9212-fbd33da9379b" 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_019d0647-9f08-7f55-9a2e-91a0901c6a96" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_019d2880-d76c-7799-9212-fbd33da9379b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_019d2880-d76c-7799-9212-fbd33da9379b_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_019d2880-d76c-7799-9212-fbd33da9379b" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_019d2880-d76c-7799-9212-fbd33da9379b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_019d2880-d76c-7c64-a2a3-9d0a3bc95846" 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_019d2880-d76c-7799-9212-fbd33da9379b" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_019d2880-d76c-7c64-a2a3-9d0a3bc95846" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout1Member_019d2880-d76c-793d-a618-0d1441a92a31" xlink:href="qtrx-20260331.xsd#qtrx_Earnout1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_019d2880-d76c-7c64-a2a3-9d0a3bc95846" xlink:to="loc_qtrx_Earnout1Member_019d2880-d76c-793d-a618-0d1441a92a31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout2Member_019d2880-d76c-781f-a282-706b941dcf01" xlink:href="qtrx-20260331.xsd#qtrx_Earnout2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_019d2880-d76c-7c64-a2a3-9d0a3bc95846" xlink:to="loc_qtrx_Earnout2Member_019d2880-d76c-781f-a282-706b941dcf01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityEquityAxis_019d2880-f7e5-79f8-878c-0564dad56bd6" 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_019d0647-9f08-7f55-9a2e-91a0901c6a96" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityEquityAxis_019d2880-f7e5-79f8-878c-0564dad56bd6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_019d2880-f7e5-79f8-878c-0564dad56bd6_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_019d2880-f7e5-79f8-878c-0564dad56bd6" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_019d2880-f7e5-79f8-878c-0564dad56bd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_019d2880-f7e5-7f1f-8478-5bcb6830bc04" 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_019d2880-f7e5-79f8-878c-0564dad56bd6" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_019d2880-f7e5-7f1f-8478-5bcb6830bc04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CallOptionMember_019d2880-f7e5-7ce5-8ee6-df358c30b85d" 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_019d2880-f7e5-7f1f-8478-5bcb6830bc04" xlink:to="loc_us-gaap_CallOptionMember_019d2880-f7e5-7ce5-8ee6-df358c30b85d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ContractWithCustomerLiabilityUnfavorableTerms_019d287a-3298-7d91-8db5-855e9a4a5dfb" xlink:href="qtrx-20260331.xsd#qtrx_ContractWithCustomerLiabilityUnfavorableTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_qtrx_ContractWithCustomerLiabilityUnfavorableTerms_019d287a-3298-7d91-8db5-855e9a4a5dfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefinitelivedIntangibleAssetsAcquired_019d67b9-a12e-7356-b0f9-32c11257dc2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefinitelivedIntangibleAssetsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_IndefinitelivedIntangibleAssetsAcquired_019d67b9-a12e-7356-b0f9-32c11257dc2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019db869-7068-7f48-9861-30df73cd8e17" 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_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019db869-7068-7f48-9861-30df73cd8e17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ContractWithCustomerLiabilityNonCashRevenueRecognized_019db869-7068-7c9a-b6e7-b060e95918f9" xlink:href="qtrx-20260331.xsd#qtrx_ContractWithCustomerLiabilityNonCashRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_qtrx_ContractWithCustomerLiabilityNonCashRevenueRecognized_019db869-7068-7c9a-b6e7-b060e95918f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenue_019db869-7068-7c42-9c07-716a866defc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_DeferredRevenue_019db869-7068-7c42-9c07-716a866defc1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019d287a-3298-7198-9faf-9828c0e77da2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019d287a-3298-7198-9faf-9828c0e77da2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019d2879-f39c-7f9d-8d51-4ecf8419eb45" 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_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019d2879-f39c-7f9d-8d51-4ecf8419eb45" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_019df1c0-1052-7ab1-9264-9e079b624417" 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_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_019df1c0-1052-7ab1-9264-9e079b624417" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_NumberOfContingentConsiderationArrangements_019d2880-d76c-76ab-ad22-81c8cdea6324" xlink:href="qtrx-20260331.xsd#qtrx_NumberOfContingentConsiderationArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_qtrx_NumberOfContingentConsiderationArrangements_019d2880-d76c-76ab-ad22-81c8cdea6324" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_019d2880-d76c-71e9-9f88-90a2072f862b" 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_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_019d2880-d76c-71e9-9f88-90a2072f862b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationContingentConsiderationPerformancePeriod_019d2880-d76c-7ec0-82e9-08d61a8b9871" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationContingentConsiderationPerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_qtrx_BusinessCombinationContingentConsiderationPerformancePeriod_019d2880-d76c-7ec0-82e9-08d61a8b9871" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019df5f7-586b-7d29-8e71-733add552471" 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_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019df5f7-586b-7d29-8e71-733add552471" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_019d2880-d76d-7388-a893-532afd76bbf1" 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_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_019d2880-d76d-7388-a893-532afd76bbf1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquitySettlementAlternativesCashAtFairValue_019d2880-f7e5-7de5-84be-c917a2d97b15" 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_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquitySettlementAlternativesCashAtFairValue_019d2880-f7e5-7de5-84be-c917a2d97b15" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OptionContractIndexedToEquityPeriod_019d2880-f7e5-76e6-9199-dc1eba81b891" xlink:href="qtrx-20260331.xsd#qtrx_OptionContractIndexedToEquityPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_qtrx_OptionContractIndexedToEquityPeriod_019d2880-f7e5-76e6-9199-dc1eba81b891" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OptionIndexedToIssuersEquityRedemptionRequirementRevenueThreshold_019d2880-f7e5-7422-98c0-3e18ab88314b" xlink:href="qtrx-20260331.xsd#qtrx_OptionIndexedToIssuersEquityRedemptionRequirementRevenueThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d2879-f39c-71bb-8af3-e81b4ca58315" xlink:to="loc_qtrx_OptionIndexedToIssuersEquityRedemptionRequirementRevenueThreshold_019d2880-f7e5-7422-98c0-3e18ab88314b" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsScheduleofFairValueoftheAggregateConsiderationPaidorPayableDetails" xlink:type="simple" xlink:href="qtrx-20260331.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_019d0647-9f08-704e-9ff1-90206e6e54b7" 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_019d0647-9f08-7c5d-9233-53ff1e8d2684" 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_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7c5d-9233-53ff1e8d2684" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019d0647-9f08-788c-bdc0-014341a3641c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7c5d-9233-53ff1e8d2684" xlink:to="loc_dei_LegalEntityAxis_019d0647-9f08-788c-bdc0-014341a3641c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019d0647-9f08-788c-bdc0-014341a3641c_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019d0647-9f08-788c-bdc0-014341a3641c" xlink:to="loc_dei_EntityDomain_019d0647-9f08-788c-bdc0-014341a3641c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019d0647-9f08-741e-8897-b62a6a4950f7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019d0647-9f08-788c-bdc0-014341a3641c" xlink:to="loc_dei_EntityDomain_019d0647-9f08-741e-8897-b62a6a4950f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-7703-9f9c-faf433f05b5c" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019d0647-9f08-741e-8897-b62a6a4950f7" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-7703-9f9c-faf433f05b5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-710d-a401-2ba146587782" 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_019d0647-9f08-7c5d-9233-53ff1e8d2684" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-710d-a401-2ba146587782" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-710d-a401-2ba146587782_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_019d0647-9f08-710d-a401-2ba146587782" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-710d-a401-2ba146587782_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-74a8-995c-173fc674734f" 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_019d0647-9f08-710d-a401-2ba146587782" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-74a8-995c-173fc674734f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-726f-8546-19d95a0f18d4" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-74a8-995c-173fc674734f" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-726f-8546-19d95a0f18d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_019d2827-9ed6-7bfb-a4ef-a5bf4f37395a" 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_019d0647-9f08-7c5d-9233-53ff1e8d2684" xlink:to="loc_us-gaap_AssetAcquisitionAxis_019d2827-9ed6-7bfb-a4ef-a5bf4f37395a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019d2827-9ed6-7bfb-a4ef-a5bf4f37395a_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_019d2827-9ed6-7bfb-a4ef-a5bf4f37395a" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019d2827-9ed6-7bfb-a4ef-a5bf4f37395a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019d2827-9ed6-72d8-a518-a885632a1212" 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_019d2827-9ed6-7bfb-a4ef-a5bf4f37395a" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019d2827-9ed6-72d8-a518-a885632a1212" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019d0647-9f08-7155-98f1-7dbf1d6b3695" 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_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_SharesOutstanding_019d0647-9f08-7155-98f1-7dbf1d6b3695" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredEquityExchangeRatio_019d0647-9f08-7cf3-8247-fd2c7cd87037" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationConsiderationTransferredEquityExchangeRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredEquityExchangeRatio_019d0647-9f08-7cf3-8247-fd2c7cd87037" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019d0647-9f08-78f1-b3a0-dc0e19f9928f" 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_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019d0647-9f08-78f1-b3a0-dc0e19f9928f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionSharePrice_019d0647-9f08-7da6-afb2-87bd5fefd703" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_BusinessAcquisitionSharePrice_019d0647-9f08-7da6-afb2-87bd5fefd703" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019d0647-9f08-7b97-883a-920d783f6e98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019d0647-9f08-7b97-883a-920d783f6e98" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019d0647-9f08-7d15-a96e-1a5d9edc7f05" 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_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019d0647-9f08-7d15-a96e-1a5d9edc7f05" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_019d0647-9f08-7d49-8409-572c4f1e202c" 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_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_019d0647-9f08-7d49-8409-572c4f1e202c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredFairValueOfReplacementEquityAwardsAttributableToPreCombinationService_019d0647-9f08-7c4a-b9b6-2604f2f8bd34" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationConsiderationTransferredFairValueOfReplacementEquityAwardsAttributableToPreCombinationService"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredFairValueOfReplacementEquityAwardsAttributableToPreCombinationService_019d0647-9f08-7c4a-b9b6-2604f2f8bd34" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019d0647-9f08-707f-a697-cbe1ea6a93ac" 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_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019d0647-9f08-707f-a697-cbe1ea6a93ac" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredFractionalSharesPricePerShare_019d0647-9f08-7731-b3b7-1ba97b03ca53" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationConsiderationTransferredFractionalSharesPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredFractionalSharesPricePerShare_019d0647-9f08-7731-b3b7-1ba97b03ca53" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationConsiderationTransferredSettlementOfEarlyTerminationLegalAndPrepaymentFees_019d0647-9f08-7718-84fd-9b79675c74a7" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationConsiderationTransferredSettlementOfEarlyTerminationLegalAndPrepaymentFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-704e-9ff1-90206e6e54b7" xlink:to="loc_qtrx_BusinessCombinationConsiderationTransferredSettlementOfEarlyTerminationLegalAndPrepaymentFees_019d0647-9f08-7718-84fd-9b79675c74a7" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsScheduleOfPreliminaryAllocationOfThePurchasePriceDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#AcquisitionsScheduleOfPreliminaryAllocationOfThePurchasePriceDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/AcquisitionsScheduleOfPreliminaryAllocationOfThePurchasePriceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-72fb-82a7-ab001d3a5d31" 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_019d0647-9f08-79a2-b061-4981f9bd7d5a" 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_019d0647-9f08-72fb-82a7-ab001d3a5d31" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-79a2-b061-4981f9bd7d5a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-7064-a368-e33cdcde62cd" 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_019d0647-9f08-79a2-b061-4981f9bd7d5a" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-7064-a368-e33cdcde62cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7064-a368-e33cdcde62cd_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_019d0647-9f08-7064-a368-e33cdcde62cd" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7064-a368-e33cdcde62cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7230-b6d9-74441e37515d" 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_019d0647-9f08-7064-a368-e33cdcde62cd" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7230-b6d9-74441e37515d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-7e98-acb1-9b944259deb9" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7230-b6d9-74441e37515d" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-7e98-acb1-9b944259deb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_019d0647-9f08-7eb8-8930-b2620f4e97da" xlink:href="qtrx-20260331.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7230-b6d9-74441e37515d" xlink:to="loc_qtrx_EmissionInc.Member_019d0647-9f08-7eb8-8930-b2620f4e97da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" 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_019d0647-9f08-72fb-82a7-ab001d3a5d31" xlink:to="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019d0647-9f08-7ade-bcbb-26dec0b7ec67" 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_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019d0647-9f08-7ade-bcbb-26dec0b7ec67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019d0647-9f08-7b28-bbea-768231c2650b" 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_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019d0647-9f08-7b28-bbea-768231c2650b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019d0647-9f08-73ae-ac53-105187e395d8" 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_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019d0647-9f08-73ae-ac53-105187e395d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredPrepaidExpenseAndOtherAsset_019d0647-9f08-7628-80e8-413f04de0268" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedAssetAcquiredPrepaidExpenseAndOtherAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredPrepaidExpenseAndOtherAsset_019d0647-9f08-7628-80e8-413f04de0268" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019d0647-9f08-72dd-9787-8b73682cecc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019d0647-9f08-72dd-9787-8b73682cecc5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019d0647-9f08-72e6-b161-f9403d9c115c" 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_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019d0647-9f08-72e6-b161-f9403d9c115c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019d0647-9f08-702f-8572-655542119336" 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_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_us-gaap_Goodwill_019d0647-9f08-702f-8572-655542119336" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredOperatingLeasesRightOfUseAssetsNet_019d0647-9f08-761c-ac52-064829ca4231" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedAssetAcquiredOperatingLeasesRightOfUseAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredOperatingLeasesRightOfUseAssetsNet_019d0647-9f08-761c-ac52-064829ca4231" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredFinanceLeasesRightOfUseAssetsNet_019d0647-9f08-789a-9c08-5fabc8b55ad9" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedAssetAcquiredFinanceLeasesRightOfUseAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredFinanceLeasesRightOfUseAssetsNet_019d0647-9f08-789a-9c08-5fabc8b55ad9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredAssetsIncludingGoodwill_019d0647-9f08-726d-889b-f9b99d6ec663" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedAssetAcquiredAssetsIncludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d0647-9f08-7884-a9c8-f130f5ff8a49" xlink:to="loc_qtrx_BusinessCombinationRecognizedAssetAcquiredAssetsIncludingGoodwill_019d0647-9f08-726d-889b-f9b99d6ec663" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" 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_019d0647-9f08-72fb-82a7-ab001d3a5d31" xlink:to="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019d0647-9f08-7d10-9654-c721bfcb337c" 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_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019d0647-9f08-7d10-9654-c721bfcb337c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedLiabilityAssumedAccruedExpensesAndOtherLiabilities_019d0647-9f08-7529-9aff-97737eb5c35d" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedLiabilityAssumedAccruedExpensesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_qtrx_BusinessCombinationRecognizedLiabilityAssumedAccruedExpensesAndOtherLiabilities_019d0647-9f08-7529-9aff-97737eb5c35d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_019d0647-9f08-7349-ac88-219035765304" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_019d0647-9f08-7349-ac88-219035765304" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilities_019d0647-9f08-7ff1-b393-8cce33d9770c" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_qtrx_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilities_019d0647-9f08-7ff1-b393-8cce33d9770c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationRecognizedLiabilityAssumedFinanceLeaseLiabilities_019d0647-9f08-729f-b94f-4df78050c69f" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationRecognizedLiabilityAssumedFinanceLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_qtrx_BusinessCombinationRecognizedLiabilityAssumedFinanceLeaseLiabilities_019d0647-9f08-729f-b94f-4df78050c69f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_019d0647-9f08-75f0-9071-cacaf10857bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_019d0647-9f08-75f0-9071-cacaf10857bf" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019d0647-9f08-799a-bec5-3a954702cb37" 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_LiabilitiesAbstract_019d0647-9f08-7ff9-b9a8-ba89b33c4694" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019d0647-9f08-799a-bec5-3a954702cb37" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/AcquisitionsScheduleOfBusinessCombinationIntangibleAssetAcquiredDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#AcquisitionsScheduleOfBusinessCombinationIntangibleAssetAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/AcquisitionsScheduleOfBusinessCombinationIntangibleAssetAcquiredDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-7752-96ce-76d9cfd1955d" 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_019d0647-9f08-7706-93a6-30705794dba2" 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_019d0647-9f08-7752-96ce-76d9cfd1955d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7706-93a6-30705794dba2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-72d7-a474-785b2d3647e9" 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_019d0647-9f08-7706-93a6-30705794dba2" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-72d7-a474-785b2d3647e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-72d7-a474-785b2d3647e9_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_019d0647-9f08-72d7-a474-785b2d3647e9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-72d7-a474-785b2d3647e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7ffb-8a1d-c051d5e90a82" 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_019d0647-9f08-72d7-a474-785b2d3647e9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7ffb-8a1d-c051d5e90a82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-7459-822b-42a2e85c6143" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7ffb-8a1d-c051d5e90a82" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019d0647-9f08-7459-822b-42a2e85c6143" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7f13-869f-53a799f37bae" 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_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7706-93a6-30705794dba2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7f13-869f-53a799f37bae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7f13-869f-53a799f37bae_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_019d0647-9f08-7f13-869f-53a799f37bae" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7f13-869f-53a799f37bae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-794f-8c5d-bab5debe3e5a" 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_019d0647-9f08-7f13-869f-53a799f37bae" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-794f-8c5d-bab5debe3e5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019d0647-9f08-776a-8674-deb4ec5eb056" 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_019d0647-9f08-794f-8c5d-bab5debe3e5a" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019d0647-9f08-776a-8674-deb4ec5eb056" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019d0647-9f08-7009-9396-192ccb806584" 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_019d0647-9f08-794f-8c5d-bab5debe3e5a" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019d0647-9f08-7009-9396-192ccb806584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7707-bd46-c74708e20932" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d0647-9f08-7706-93a6-30705794dba2" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7707-bd46-c74708e20932" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7707-bd46-c74708e20932_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7707-bd46-c74708e20932" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7707-bd46-c74708e20932_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7069-9036-518ad5624329" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7707-bd46-c74708e20932" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7069-9036-518ad5624329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_019d0647-9f08-745b-b0d5-1dd880c18698" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7069-9036-518ad5624329" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_019d0647-9f08-745b-b0d5-1dd880c18698" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019d0647-9f08-7973-9109-d0799c7935fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-7752-96ce-76d9cfd1955d" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019d0647-9f08-7973-9109-d0799c7935fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019d0647-9f08-74d8-9967-e20b83071176" 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_019d0647-9f08-7752-96ce-76d9cfd1955d" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019d0647-9f08-74d8-9967-e20b83071176" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefinitelivedIntangibleAssetsAcquired_019d0647-9f08-7bb0-810a-f2254f36b8b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefinitelivedIntangibleAssetsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d0647-9f08-7752-96ce-76d9cfd1955d" xlink:to="loc_us-gaap_IndefinitelivedIntangibleAssetsAcquired_019d0647-9f08-7bb0-810a-f2254f36b8b6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/GoodwillandIntangibleAssetsScheduleofGoodwillDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#GoodwillandIntangibleAssetsScheduleofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/GoodwillandIntangibleAssetsScheduleofGoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019db87f-92d5-7f91-a2c0-6f71926df100" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019db87f-92d5-77ea-8e6e-5af7beaada06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019db87f-92d5-7f91-a2c0-6f71926df100" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019db87f-92d5-77ea-8e6e-5af7beaada06" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019db87f-92d5-70a1-ae37-6bea66a516d7" 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_ScheduleOfFiniteLivedIntangibleAssetsTable_019db87f-92d5-77ea-8e6e-5af7beaada06" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019db87f-92d5-70a1-ae37-6bea66a516d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db87f-92d5-70a1-ae37-6bea66a516d7_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_019db87f-92d5-70a1-ae37-6bea66a516d7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db87f-92d5-70a1-ae37-6bea66a516d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db87f-92d5-7eb7-ab46-120d9a752ebd" 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_019db87f-92d5-70a1-ae37-6bea66a516d7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db87f-92d5-7eb7-ab46-120d9a752ebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_019db87f-92d5-7765-971a-06e85f29a380" xlink:href="qtrx-20260331.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db87f-92d5-7eb7-ab46-120d9a752ebd" xlink:to="loc_qtrx_EmissionInc.Member_019db87f-92d5-7765-971a-06e85f29a380" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019db87f-92d5-71f2-adf7-773f9aa961ba" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db87f-92d5-7eb7-ab46-120d9a752ebd" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019db87f-92d5-71f2-adf7-773f9aa961ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_019d0647-9f08-7d8d-8d0c-7e30fb6f018e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019db87f-92d5-7f91-a2c0-6f71926df100" xlink:to="loc_us-gaap_GoodwillRollForward_019d0647-9f08-7d8d-8d0c-7e30fb6f018e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019d0647-9f08-7ee2-be53-3c4c23c3f1ed" 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_GoodwillRollForward_019d0647-9f08-7d8d-8d0c-7e30fb6f018e" xlink:to="loc_us-gaap_Goodwill_019d0647-9f08-7ee2-be53-3c4c23c3f1ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_019d0647-9f08-792d-afea-7575f36a8d7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019d0647-9f08-7d8d-8d0c-7e30fb6f018e" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_019d0647-9f08-792d-afea-7575f36a8d7f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019db87b-6e77-7bc9-9de7-bab3ae64a1ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019d0647-9f08-7d8d-8d0c-7e30fb6f018e" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019db87b-6e77-7bc9-9de7-bab3ae64a1ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019df1da-51c8-7a02-b3dc-f71449e9473f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019d0647-9f08-7d8d-8d0c-7e30fb6f018e" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019df1da-51c8-7a02-b3dc-f71449e9473f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019d0647-9f08-7d11-adc2-f9cbe501682e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019d0647-9f08-756c-9cc7-c21474797113" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019d0647-9f08-756c-9cc7-c21474797113" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d0647-9f08-7ea5-9315-f3d01be81288" 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_ScheduleOfFiniteLivedIntangibleAssetsTable_019d0647-9f08-756c-9cc7-c21474797113" xlink:to="loc_srt_RangeAxis_019d0647-9f08-7ea5-9315-f3d01be81288" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d0647-9f08-7ea5-9315-f3d01be81288_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_019d0647-9f08-7ea5-9315-f3d01be81288" xlink:to="loc_srt_RangeMember_019d0647-9f08-7ea5-9315-f3d01be81288_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d0647-9f08-7e55-a96e-2b9240d5f532" 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_019d0647-9f08-7ea5-9315-f3d01be81288" xlink:to="loc_srt_RangeMember_019d0647-9f08-7e55-a96e-2b9240d5f532" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019d0647-9f08-7198-ba63-28e88d900267" 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_019d0647-9f08-7e55-a96e-2b9240d5f532" xlink:to="loc_srt_MinimumMember_019d0647-9f08-7198-ba63-28e88d900267" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d0647-9f08-7571-a670-81c7b2a73edd" 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_019d0647-9f08-7e55-a96e-2b9240d5f532" xlink:to="loc_srt_MaximumMember_019d0647-9f08-7571-a670-81c7b2a73edd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7f74-bc28-d5478aef1f64" 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_ScheduleOfFiniteLivedIntangibleAssetsTable_019d0647-9f08-756c-9cc7-c21474797113" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7f74-bc28-d5478aef1f64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7f74-bc28-d5478aef1f64_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_019d0647-9f08-7f74-bc28-d5478aef1f64" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7f74-bc28-d5478aef1f64_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7906-a51e-baa624b5e804" 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_019d0647-9f08-7f74-bc28-d5478aef1f64" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7906-a51e-baa624b5e804" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019d0647-9f08-73a4-afa5-06aed87b307e" 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_019d0647-9f08-7906-a51e-baa624b5e804" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019d0647-9f08-73a4-afa5-06aed87b307e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_KnowHowMember_019d0647-9f08-72f6-a9d0-1f4ff2c30ca6" xlink:href="qtrx-20260331.xsd#qtrx_KnowHowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7906-a51e-baa624b5e804" xlink:to="loc_qtrx_KnowHowMember_019d0647-9f08-72f6-a9d0-1f4ff2c30ca6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019d0647-9f08-791c-b151-439dd1f637ac" 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_019d0647-9f08-7906-a51e-baa624b5e804" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019d0647-9f08-791c-b151-439dd1f637ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7e23-bce7-8e1f39d1dcc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019d0647-9f08-756c-9cc7-c21474797113" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7e23-bce7-8e1f39d1dcc2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7e23-bce7-8e1f39d1dcc2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7e23-bce7-8e1f39d1dcc2" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-7e23-bce7-8e1f39d1dcc2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-78a9-9d69-17667108223b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019d0647-9f08-7e23-bce7-8e1f39d1dcc2" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-78a9-9d69-17667108223b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_019d0647-9f08-7389-b1e4-c72bda3bb79b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019d0647-9f08-78a9-9d69-17667108223b" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_019d0647-9f08-7389-b1e4-c72bda3bb79b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019d0647-9f08-7184-a090-84a90e0a3a10" 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_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019d0647-9f08-7184-a090-84a90e0a3a10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019d0647-9f08-748e-93fb-2f8abdcc04ef" 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_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019d0647-9f08-748e-93fb-2f8abdcc04ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019d0647-9f08-767e-84b7-d57909b1a0c5" 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_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019d0647-9f08-767e-84b7-d57909b1a0c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments_019d0647-9f08-74e8-a659-17f423208c23" xlink:href="qtrx-20260331.xsd#qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments_019d0647-9f08-74e8-a659-17f423208c23" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019d0647-9f08-7fe2-91ea-19c1c781ba68" 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_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019d0647-9f08-7fe2-91ea-19c1c781ba68" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_019d0647-9f08-787c-94e9-bd18c336fc23" 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_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_019d0647-9f08-787c-94e9-bd18c336fc23" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019d0647-9f08-7659-b495-8fc3eb6c7b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019d0647-9f08-7659-b495-8fc3eb6c7b9e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019d0647-9f08-7194-8e34-03437f6c26d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019d0647-9f08-7194-8e34-03437f6c26d6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019d0647-9f08-7397-91c2-7afcfe0e53f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments_019d0647-9f08-71f0-bf39-89f1becfe7f7" xlink:href="qtrx-20260331.xsd#qtrx_FiniteLivedIntangibleAssetsCumulativeTranslationAdjustments"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019d0647-9f08-7fb9-912b-73f9bedf8b97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019d0647-9f08-775c-91ad-bdd5217939ca" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019d0647-9f08-7fb9-912b-73f9bedf8b97" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RevenueandRelatedMattersScheduleofDisaggregatedRevenueDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#RevenueandRelatedMattersScheduleofDisaggregatedRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/RevenueandRelatedMattersScheduleofDisaggregatedRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019d0647-9f08-7dfb-ac15-05679ff81186" 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_019d0647-9f08-7af6-92a2-bb6769845739" 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_019d0647-9f08-7dfb-ac15-05679ff81186" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019d0647-9f08-7af6-92a2-bb6769845739" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d0647-9f08-77f9-be0d-224d21c9f7b6" 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_019d0647-9f08-7af6-92a2-bb6769845739" xlink:to="loc_srt_ProductOrServiceAxis_019d0647-9f08-77f9-be0d-224d21c9f7b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d0647-9f08-77f9-be0d-224d21c9f7b6_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_019d0647-9f08-77f9-be0d-224d21c9f7b6" xlink:to="loc_srt_ProductsAndServicesDomain_019d0647-9f08-77f9-be0d-224d21c9f7b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d0647-9f08-703e-9bba-7cedd095f985" 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_019d0647-9f08-77f9-be0d-224d21c9f7b6" xlink:to="loc_srt_ProductsAndServicesDomain_019d0647-9f08-703e-9bba-7cedd095f985" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019d0647-9f08-75c5-ae64-7ad237d786f1" 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_019d0647-9f08-703e-9bba-7cedd095f985" xlink:to="loc_us-gaap_ProductMember_019d0647-9f08-75c5-ae64-7ad237d786f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_InstrumentsMember_019d0647-9f08-74ea-8c11-0581cc11a374" xlink:href="qtrx-20260331.xsd#qtrx_InstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019d0647-9f08-75c5-ae64-7ad237d786f1" xlink:to="loc_qtrx_InstrumentsMember_019d0647-9f08-74ea-8c11-0581cc11a374" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ConsumableAndOtherProductsMember_019d0647-9f08-7e07-a589-9229265f1398" xlink:href="qtrx-20260331.xsd#qtrx_ConsumableAndOtherProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019d0647-9f08-75c5-ae64-7ad237d786f1" xlink:to="loc_qtrx_ConsumableAndOtherProductsMember_019d0647-9f08-7e07-a589-9229265f1398" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_SimoaProductRevenueMember_019d2892-ab3b-775f-a40b-6fa1b17ad2b9" xlink:href="qtrx-20260331.xsd#qtrx_SimoaProductRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019d0647-9f08-75c5-ae64-7ad237d786f1" xlink:to="loc_qtrx_SimoaProductRevenueMember_019d2892-ab3b-775f-a40b-6fa1b17ad2b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_SpatialProductRevenueMember_019d2892-ab3b-7579-a81c-348951a64f8a" xlink:href="qtrx-20260331.xsd#qtrx_SpatialProductRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019d0647-9f08-75c5-ae64-7ad237d786f1" xlink:to="loc_qtrx_SpatialProductRevenueMember_019d2892-ab3b-7579-a81c-348951a64f8a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:href="qtrx-20260331.xsd#qtrx_ServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d0647-9f08-703e-9bba-7cedd095f985" xlink:to="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ResearchServicesMember_019d0647-9f08-7198-9cc5-e9e4cc0b93be" xlink:href="qtrx-20260331.xsd#qtrx_ResearchServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:to="loc_qtrx_ResearchServicesMember_019d0647-9f08-7198-9cc5-e9e4cc0b93be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceTypeWarrantiesMember_019d0647-9f08-7644-9418-1816955ac9e2" xlink:href="qtrx-20260331.xsd#qtrx_ServiceTypeWarrantiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:to="loc_qtrx_ServiceTypeWarrantiesMember_019d0647-9f08-7644-9418-1816955ac9e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_OtherServicesMember_019d0647-9f08-7657-a2dc-95a24cb6eb08" xlink:href="qtrx-20260331.xsd#qtrx_OtherServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:to="loc_qtrx_OtherServicesMember_019d0647-9f08-7657-a2dc-95a24cb6eb08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_SimoaServiceAndOtherRevenueMember_019d2892-ab3b-7e62-9423-91be1683f256" xlink:href="qtrx-20260331.xsd#qtrx_SimoaServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:to="loc_qtrx_SimoaServiceAndOtherRevenueMember_019d2892-ab3b-7e62-9423-91be1683f256" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_SpatialServiceAndOtherRevenueMember_019d2892-ab3b-76a0-b167-f124fb75dfcd" xlink:href="qtrx-20260331.xsd#qtrx_SpatialServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9f08-7874-b80a-d0c5005af059" xlink:to="loc_qtrx_SpatialServiceAndOtherRevenueMember_019d2892-ab3b-76a0-b167-f124fb75dfcd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseAndServiceMember_019db88d-803b-7447-af15-b5069b0f0a6b" 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_019d0647-9f08-703e-9bba-7cedd095f985" xlink:to="loc_us-gaap_LicenseAndServiceMember_019db88d-803b-7447-af15-b5069b0f0a6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019d0647-9f08-7897-a194-d92821edfd5b" 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_019d0647-9f08-7af6-92a2-bb6769845739" xlink:to="loc_srt_StatementGeographicalAxis_019d0647-9f08-7897-a194-d92821edfd5b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019d0647-9f08-7897-a194-d92821edfd5b_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_019d0647-9f08-7897-a194-d92821edfd5b" xlink:to="loc_srt_SegmentGeographicalDomain_019d0647-9f08-7897-a194-d92821edfd5b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019d0647-9f08-71cc-8456-7db817fda930" 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_019d0647-9f08-7897-a194-d92821edfd5b" xlink:to="loc_srt_SegmentGeographicalDomain_019d0647-9f08-71cc-8456-7db817fda930" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_019d0647-9f08-74af-a52d-aaed25ba2397" 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_019d0647-9f08-71cc-8456-7db817fda930" xlink:to="loc_srt_NorthAmericaMember_019d0647-9f08-74af-a52d-aaed25ba2397" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_019d0647-9f08-7609-9d87-3c92cda67c8e" 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_019d0647-9f08-71cc-8456-7db817fda930" xlink:to="loc_us-gaap_EMEAMember_019d0647-9f08-7609-9d87-3c92cda67c8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_019d0647-9f08-7ce3-a923-5be90fe54037" 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_019d0647-9f08-71cc-8456-7db817fda930" xlink:to="loc_srt_AsiaPacificMember_019d0647-9f08-7ce3-a923-5be90fe54037" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019d0647-9f08-709a-8a43-cbd8e717100b" 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_019d0647-9f08-7dfb-ac15-05679ff81186" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019d0647-9f08-709a-8a43-cbd8e717100b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RevenueandRelatedMattersNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20260331.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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" 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_019d0647-9f08-7346-a917-51ac01aa6e67" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019d2896-da0e-7261-b472-f7b3fd99c4f5" 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_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019d2896-da0e-7261-b472-f7b3fd99c4f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d2896-da0e-7dfd-bb35-7f6c780da143" 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_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:to="loc_srt_ProductOrServiceAxis_019d2896-da0e-7dfd-bb35-7f6c780da143" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7dfd-bb35-7f6c780da143_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_019d2896-da0e-7dfd-bb35-7f6c780da143" xlink:to="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7dfd-bb35-7f6c780da143_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7ede-b865-45634fc43738" 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_019d2896-da0e-7dfd-bb35-7f6c780da143" xlink:to="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7ede-b865-45634fc43738" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_019d2896-da0e-7398-a16b-719c97571b93" xlink:href="qtrx-20260331.xsd#qtrx_UndeliveredLicensesOfIntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7ede-b865-45634fc43738" xlink:to="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_019d2896-da0e-7398-a16b-719c97571b93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019db88c-6891-7b6d-b867-e5ea321df44a" 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_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019db88c-6891-7b6d-b867-e5ea321df44a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-7b6d-b867-e5ea321df44a_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_019db88c-6891-7b6d-b867-e5ea321df44a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-7b6d-b867-e5ea321df44a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-70d8-9fe5-d1d23b7d2c76" 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_019db88c-6891-7b6d-b867-e5ea321df44a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-70d8-9fe5-d1d23b7d2c76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019db88c-6891-7263-b2bd-5beb130577e0" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-70d8-9fe5-d1d23b7d2c76" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019db88c-6891-7263-b2bd-5beb130577e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_019d2896-bd3a-7cf5-864e-310db501937e" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_019d2896-bd3a-7cf5-864e-310db501937e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019d2896-bd3a-7dc7-a0a5-4eb7c4e2dcbe" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019d2896-bd3a-7dc7-a0a5-4eb7c4e2dcbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenue_019d67ed-46ab-70a0-a241-50673f2179c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_DeferredRevenue_019d67ed-46ab-70a0-a241-50673f2179c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019d2896-da0e-7b4a-ae73-a05ce95f91f9" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019d2896-da0e-7b4a-ae73-a05ce95f91f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d2896-da0e-7a0f-ac7b-8a7a27402654" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d2896-da0e-7a0f-ac7b-8a7a27402654" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/RevenueandRelatedMattersNarrativeDetails_1" xlink:type="simple" xlink:href="qtrx-20260331.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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" 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_019d0647-9f08-7346-a917-51ac01aa6e67" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d2896-da0e-7dfd-bb35-7f6c780da143" 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_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:to="loc_srt_ProductOrServiceAxis_019d2896-da0e-7dfd-bb35-7f6c780da143" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7dfd-bb35-7f6c780da143_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_019d2896-da0e-7dfd-bb35-7f6c780da143" xlink:to="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7dfd-bb35-7f6c780da143_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7ede-b865-45634fc43738" 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_019d2896-da0e-7dfd-bb35-7f6c780da143" xlink:to="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7ede-b865-45634fc43738" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_019d2896-da0e-7398-a16b-719c97571b93" xlink:href="qtrx-20260331.xsd#qtrx_UndeliveredLicensesOfIntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d2896-da0e-7ede-b865-45634fc43738" xlink:to="loc_qtrx_UndeliveredLicensesOfIntellectualPropertyMember_019d2896-da0e-7398-a16b-719c97571b93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019db88c-6891-7b6d-b867-e5ea321df44a" 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_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d0647-9f08-7346-a917-51ac01aa6e67" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019db88c-6891-7b6d-b867-e5ea321df44a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-7b6d-b867-e5ea321df44a_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_019db88c-6891-7b6d-b867-e5ea321df44a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-7b6d-b867-e5ea321df44a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-70d8-9fe5-d1d23b7d2c76" 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_019db88c-6891-7b6d-b867-e5ea321df44a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-70d8-9fe5-d1d23b7d2c76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_AkoyaBiosciencesInc.Member_019db88c-6891-7263-b2bd-5beb130577e0" xlink:href="qtrx-20260331.xsd#qtrx_AkoyaBiosciencesInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019db88c-6891-70d8-9fe5-d1d23b7d2c76" xlink:to="loc_qtrx_AkoyaBiosciencesInc.Member_019db88c-6891-7263-b2bd-5beb130577e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_019d2896-bd3a-7cf5-864e-310db501937e" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_019d2896-bd3a-7cf5-864e-310db501937e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019d2896-bd3a-7dc7-a0a5-4eb7c4e2dcbe" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019d2896-bd3a-7dc7-a0a5-4eb7c4e2dcbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenue_019d67ed-46ab-70a0-a241-50673f2179c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_DeferredRevenue_019d67ed-46ab-70a0-a241-50673f2179c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019d2896-da0e-7b4a-ae73-a05ce95f91f9" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019d2896-da0e-7b4a-ae73-a05ce95f91f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d2896-da0e-7a0f-ac7b-8a7a27402654" 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_019d2896-bd3a-77b9-9cfa-7ecc46d4dad4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d2896-da0e-7a0f-ac7b-8a7a27402654" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/MarketableSecuritiesScheduleofAmortizedCostGrossUnrealizedGainsGrossUnrealizedLossesandFairValueDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#MarketableSecuritiesScheduleofAmortizedCostGrossUnrealizedGainsGrossUnrealizedLossesandFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/MarketableSecuritiesScheduleofAmortizedCostGrossUnrealizedGainsGrossUnrealizedLossesandFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019d0647-9f08-7600-ba96-a8fe25b96fcf" 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_019d0647-9f08-7731-a5e5-7a7412483417" 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_019d0647-9f08-7600-ba96-a8fe25b96fcf" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019d0647-9f08-7731-a5e5-7a7412483417" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d0647-9f08-7435-81fe-e8ba37e483c0" 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_019d0647-9f08-7731-a5e5-7a7412483417" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d0647-9f08-7435-81fe-e8ba37e483c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-7435-81fe-e8ba37e483c0_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_019d0647-9f08-7435-81fe-e8ba37e483c0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-7435-81fe-e8ba37e483c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-7510-bf83-48af3e91f355" 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_019d0647-9f08-7435-81fe-e8ba37e483c0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-7510-bf83-48af3e91f355" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019d0647-9f08-77e9-a14f-cae55f4d2365" 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_019d0647-9f08-7510-bf83-48af3e91f355" xlink:to="loc_us-gaap_CommercialPaperMember_019d0647-9f08-77e9-a14f-cae55f4d2365" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019d0647-9f08-7c83-b564-bd45fbd3769a" 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_019d0647-9f08-7510-bf83-48af3e91f355" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019d0647-9f08-7c83-b564-bd45fbd3769a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019d0647-9f08-7757-99c5-9a83bbd10257" 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_019d0647-9f08-7510-bf83-48af3e91f355" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019d0647-9f08-7757-99c5-9a83bbd10257" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019d0647-9f08-7ded-837b-4efbd799c421" 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_019d0647-9f08-7510-bf83-48af3e91f355" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019d0647-9f08-7ded-837b-4efbd799c421" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss_019d0647-9f08-729b-921a-a160ec01bd15" 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_019d0647-9f08-7600-ba96-a8fe25b96fcf" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss_019d0647-9f08-729b-921a-a160ec01bd15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain_019d0647-9f08-788e-a541-469575c2dd73" 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_019d0647-9f08-7600-ba96-a8fe25b96fcf" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain_019d0647-9f08-788e-a541-469575c2dd73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss_019d0647-9f08-7c3b-a5be-49397a585e41" 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_019d0647-9f08-7600-ba96-a8fe25b96fcf" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss_019d0647-9f08-7c3b-a5be-49397a585e41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue_019d0647-9f08-7512-955d-baabcc91a3aa" 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_019d0647-9f08-7600-ba96-a8fe25b96fcf" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue_019d0647-9f08-7512-955d-baabcc91a3aa" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/MarketableSecuritiesScheduleofFairValueandGrossUnrealizedLossesDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#MarketableSecuritiesScheduleofFairValueandGrossUnrealizedLossesDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/MarketableSecuritiesScheduleofFairValueandGrossUnrealizedLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019d0647-9f08-710d-a5e0-2296bd0d7629" 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_019d0647-9f08-7fe8-b195-d145d800255e" 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_019d0647-9f08-710d-a5e0-2296bd0d7629" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019d0647-9f08-7fe8-b195-d145d800255e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d0647-9f08-715a-895e-d7177a57058b" 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_019d0647-9f08-7fe8-b195-d145d800255e" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d0647-9f08-715a-895e-d7177a57058b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-715a-895e-d7177a57058b_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_019d0647-9f08-715a-895e-d7177a57058b" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-715a-895e-d7177a57058b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-7b6f-8d0d-d92302dadc0e" 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_019d0647-9f08-715a-895e-d7177a57058b" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d0647-9f08-7b6f-8d0d-d92302dadc0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019d0647-9f08-775d-8913-e79dcb75211a" 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_019d0647-9f08-7b6f-8d0d-d92302dadc0e" xlink:to="loc_us-gaap_CommercialPaperMember_019d0647-9f08-775d-8913-e79dcb75211a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019d0647-9f08-7fdd-a954-f33dc5bfae59" 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_019d0647-9f08-7b6f-8d0d-d92302dadc0e" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019d0647-9f08-7fdd-a954-f33dc5bfae59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019d0647-9f08-723b-a4fb-3a6fcc250978" 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_019d0647-9f08-7b6f-8d0d-d92302dadc0e" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019d0647-9f08-723b-a4fb-3a6fcc250978" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019d0647-9f08-791f-b2c9-5f74c0228e74" 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_019d0647-9f08-710d-a5e0-2296bd0d7629" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019d0647-9f08-791f-b2c9-5f74c0228e74" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019d0647-9f08-7b1d-8892-89014e06e523" 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_019d0647-9f08-710d-a5e0-2296bd0d7629" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019d0647-9f08-7b1d-8892-89014e06e523" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019d0647-9f08-7172-aa3a-11b878432949" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019d0647-9f08-710d-a5e0-2296bd0d7629" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019d0647-9f08-7172-aa3a-11b878432949" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019d0647-9f08-7b1f-b0ee-b9bff7de26cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019d0647-9f08-710d-a5e0-2296bd0d7629" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019d0647-9f08-7b1f-b0ee-b9bff7de26cf" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/FairValueofFinancialInstrumentsScheduleofFairValueofFinancialAssetsDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#FairValueofFinancialInstrumentsScheduleofFairValueofFinancialAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/FairValueofFinancialInstrumentsScheduleofFairValueofFinancialAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d0647-9f08-7646-ab13-a53439e6485d" 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_019d0647-9f08-7e14-a36b-cbf74f9456a3" 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_019d0647-9f08-7646-ab13-a53439e6485d" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019d0647-9f08-7e14-a36b-cbf74f9456a3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d0647-9f08-7233-96a3-f54e5acab4b0" 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_019d0647-9f08-7e14-a36b-cbf74f9456a3" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d0647-9f08-7233-96a3-f54e5acab4b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d0647-9f08-7233-96a3-f54e5acab4b0_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_019d0647-9f08-7233-96a3-f54e5acab4b0" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d0647-9f08-7233-96a3-f54e5acab4b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d0647-9f08-7b3b-92a8-03b2b3ec1589" 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_019d0647-9f08-7233-96a3-f54e5acab4b0" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d0647-9f08-7b3b-92a8-03b2b3ec1589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019d0647-9f08-77bc-aa00-3f520de0144a" 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_019d0647-9f08-7b3b-92a8-03b2b3ec1589" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019d0647-9f08-77bc-aa00-3f520de0144a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019d0647-9f08-7756-920f-e839a08dd3ae" 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_019d0647-9f08-7b3b-92a8-03b2b3ec1589" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019d0647-9f08-7756-920f-e839a08dd3ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019d0647-9f08-7e2f-820f-b7734c479ab7" 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_019d0647-9f08-7b3b-92a8-03b2b3ec1589" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019d0647-9f08-7e2f-820f-b7734c479ab7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019d0647-9f08-78e7-bcc9-99b2fa34b06c" 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_019d0647-9f08-7e14-a36b-cbf74f9456a3" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019d0647-9f08-78e7-bcc9-99b2fa34b06c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019d0647-9f08-78e7-bcc9-99b2fa34b06c_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_019d0647-9f08-78e7-bcc9-99b2fa34b06c" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019d0647-9f08-78e7-bcc9-99b2fa34b06c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019d0647-9f08-7da1-9541-f6b7afd24a6e" 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_019d0647-9f08-78e7-bcc9-99b2fa34b06c" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019d0647-9f08-7da1-9541-f6b7afd24a6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019d0647-9f08-709b-b370-5cbbb4b4114d" 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_019d0647-9f08-7da1-9541-f6b7afd24a6e" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019d0647-9f08-709b-b370-5cbbb4b4114d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019d0647-9f08-7ed0-9489-2deffa7f80a4" 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_019d0647-9f08-7da1-9541-f6b7afd24a6e" xlink:to="loc_us-gaap_CommercialPaperMember_019d0647-9f08-7ed0-9489-2deffa7f80a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019d0647-9f08-77ec-bea9-61fc3681ed97" 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_019d0647-9f08-7da1-9541-f6b7afd24a6e" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019d0647-9f08-77ec-bea9-61fc3681ed97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019d0647-9f08-7b13-994b-fae7b16d8798" 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_019d0647-9f08-7da1-9541-f6b7afd24a6e" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019d0647-9f08-7b13-994b-fae7b16d8798" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019d0647-9f08-7111-935e-f7fb561497b6" 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_019d0647-9f08-7da1-9541-f6b7afd24a6e" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019d0647-9f08-7111-935e-f7fb561497b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019d0647-9f08-7a76-a131-854f79faf2b6" 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_019d0647-9f08-7646-ab13-a53439e6485d" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019d0647-9f08-7a76-a131-854f79faf2b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019d0647-9f08-7c18-b0e6-fbd2802adc1b" 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_019d0647-9f08-7a76-a131-854f79faf2b6" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019d0647-9f08-7c18-b0e6-fbd2802adc1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_019d0647-9f08-77c6-917d-36d1fa9bbd95" 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_019d0647-9f08-7a76-a131-854f79faf2b6" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_019d0647-9f08-77c6-917d-36d1fa9bbd95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019d0647-9f08-7d91-8579-0cdb1dc09b29" 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_019d0647-9f08-7a76-a131-854f79faf2b6" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019d0647-9f08-7d91-8579-0cdb1dc09b29" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019d0647-9f08-7cf5-9ac5-d6c2e183c3fc" 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_019d0647-9f08-7a76-a131-854f79faf2b6" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019d0647-9f08-7cf5-9ac5-d6c2e183c3fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019d0647-9f08-7b99-98d4-4b96dcd4d47e" 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_019d0647-9f08-7a76-a131-854f79faf2b6" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019d0647-9f08-7b99-98d4-4b96dcd4d47e" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/FairValueofFinancialInstrumentsScheduleofFairValueLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#FairValueofFinancialInstrumentsScheduleofFairValueLiabilitiesMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/FairValueofFinancialInstrumentsScheduleofFairValueLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d0647-9f08-78c5-b194-860968974f8b" 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_019d0647-9f08-7bf2-a132-15edce4ebd86" 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_019d0647-9f08-78c5-b194-860968974f8b" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019d0647-9f08-7bf2-a132-15edce4ebd86" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-7530-b7ad-c8655d20e0d1" 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_019d0647-9f08-7bf2-a132-15edce4ebd86" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d0647-9f08-7530-b7ad-c8655d20e0d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7530-b7ad-c8655d20e0d1_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_019d0647-9f08-7530-b7ad-c8655d20e0d1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-7530-b7ad-c8655d20e0d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-707e-bee8-feef46c535e4" 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_019d0647-9f08-7530-b7ad-c8655d20e0d1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-707e-bee8-feef46c535e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_019d0647-9f08-7395-ab01-2e743561f0bb" xlink:href="qtrx-20260331.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-707e-bee8-feef46c535e4" xlink:to="loc_qtrx_EmissionInc.Member_019d0647-9f08-7395-ab01-2e743561f0bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_PKILicenseMember_019d0647-9f08-7e8c-a72e-2ea6ba7fa6b5" xlink:href="qtrx-20260331.xsd#qtrx_PKILicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d0647-9f08-707e-bee8-feef46c535e4" xlink:to="loc_qtrx_PKILicenseMember_019d0647-9f08-7e8c-a72e-2ea6ba7fa6b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d0647-9f08-71c2-9be6-6e3407885141" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d0647-9f08-78c5-b194-860968974f8b" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d0647-9f08-71c2-9be6-6e3407885141" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019d0647-9f08-738c-80f5-c2b678ad7cff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d0647-9f08-71c2-9be6-6e3407885141" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019d0647-9f08-738c-80f5-c2b678ad7cff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_019d67f2-9ce0-71d7-a3d0-51a9fd9f726c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d0647-9f08-71c2-9be6-6e3407885141" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_019d67f2-9ce0-71d7-a3d0-51a9fd9f726c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019d0647-9f08-734d-a502-1f92cdef981b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d0647-9f08-71c2-9be6-6e3407885141" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019d0647-9f08-734d-a502-1f92cdef981b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019d0647-9f08-7660-9803-e3753b198a8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_BusinessCombinationContingentConsiderationPaymentPeriod_019d0647-9f08-7e33-8709-5630cfb079d8" xlink:href="qtrx-20260331.xsd#qtrx_BusinessCombinationContingentConsiderationPaymentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d0647-9f08-78c5-b194-860968974f8b" xlink:to="loc_qtrx_BusinessCombinationContingentConsiderationPaymentPeriod_019d0647-9f08-7e33-8709-5630cfb079d8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20260331.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_019d28a3-f3ce-7cff-9ac6-75c81a062374" 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_019d0647-9f08-79e3-8fe9-9836faeeb8cf" 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_019d28a3-f3ce-7cff-9ac6-75c81a062374" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0647-9f08-79e3-8fe9-9836faeeb8cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d28a3-f3ce-7f84-9e29-941b67e25b59" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0647-9f08-79e3-8fe9-9836faeeb8cf" xlink:to="loc_srt_RangeAxis_019d28a3-f3ce-7f84-9e29-941b67e25b59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d28a3-f3ce-7f84-9e29-941b67e25b59_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_019d28a3-f3ce-7f84-9e29-941b67e25b59" xlink:to="loc_srt_RangeMember_019d28a3-f3ce-7f84-9e29-941b67e25b59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d28a3-f3ce-7d9f-816d-87c76c381a22" 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_019d28a3-f3ce-7f84-9e29-941b67e25b59" xlink:to="loc_srt_RangeMember_019d28a3-f3ce-7d9f-816d-87c76c381a22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019d28a3-f3ce-7776-a07f-36280ca3dc5e" 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_019d28a3-f3ce-7d9f-816d-87c76c381a22" xlink:to="loc_srt_MinimumMember_019d28a3-f3ce-7776-a07f-36280ca3dc5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d28a3-f3ce-7341-b3f9-ced6f172dc0c" 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_019d28a3-f3ce-7d9f-816d-87c76c381a22" xlink:to="loc_srt_MaximumMember_019d28a3-f3ce-7341-b3f9-ced6f172dc0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d28a3-f3ce-72a8-9aa3-13953d7d273c" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0647-9f08-79e3-8fe9-9836faeeb8cf" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d28a3-f3ce-72a8-9aa3-13953d7d273c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d28a3-f3ce-72a8-9aa3-13953d7d273c_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_019d28a3-f3ce-72a8-9aa3-13953d7d273c" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d28a3-f3ce-72a8-9aa3-13953d7d273c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d28a3-f3ce-73bc-bf61-7aad58b91c2e" 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_019d28a3-f3ce-72a8-9aa3-13953d7d273c" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d28a3-f3ce-73bc-bf61-7aad58b91c2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EmissionInc.Member_019d28a3-f3ce-7e7b-b877-e5a26aa46993" xlink:href="qtrx-20260331.xsd#qtrx_EmissionInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d28a3-f3ce-73bc-bf61-7aad58b91c2e" xlink:to="loc_qtrx_EmissionInc.Member_019d28a3-f3ce-7e7b-b877-e5a26aa46993" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_019d28a3-f3ce-72fe-8f8c-6ec58b7339bc" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0647-9f08-79e3-8fe9-9836faeeb8cf" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_019d28a3-f3ce-72fe-8f8c-6ec58b7339bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_019d28a3-f3ce-72fe-8f8c-6ec58b7339bc_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_019d28a3-f3ce-72fe-8f8c-6ec58b7339bc" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_019d28a3-f3ce-72fe-8f8c-6ec58b7339bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_019d28a3-f3ce-7990-bd08-4e431feadd29" 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_019d28a3-f3ce-72fe-8f8c-6ec58b7339bc" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_019d28a3-f3ce-7990-bd08-4e431feadd29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_Earnout2Member_019d28a3-f3ce-7596-91ee-6a50cd0abaa9" xlink:href="qtrx-20260331.xsd#qtrx_Earnout2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_019d28a3-f3ce-7990-bd08-4e431feadd29" xlink:to="loc_qtrx_Earnout2Member_019d28a3-f3ce-7596-91ee-6a50cd0abaa9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019d28a3-f3ce-7012-b0bc-35f263ef539f" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d28a3-f3ce-7cff-9ac6-75c81a062374" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019d28a3-f3ce-7012-b0bc-35f263ef539f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockholdersEquityDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#StockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d0647-9fcc-7883-8cd9-1ed2d46657a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019d0647-9fcc-7513-8491-aaf8965e89a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d0647-9fcc-7883-8cd9-1ed2d46657a3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019d0647-9fcc-7513-8491-aaf8965e89a7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d0647-9fcc-7b82-a37f-1ce9618e2d4b" 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_AccumulatedOtherComprehensiveIncomeLossTable_019d0647-9fcc-7513-8491-aaf8965e89a7" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d0647-9fcc-7b82-a37f-1ce9618e2d4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d0647-9fcc-7b82-a37f-1ce9618e2d4b_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_019d0647-9fcc-7b82-a37f-1ce9618e2d4b" xlink:to="loc_us-gaap_EquityComponentDomain_019d0647-9fcc-7b82-a37f-1ce9618e2d4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d0647-9fcc-7134-94e4-ac45c88fc0f4" 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_019d0647-9fcc-7b82-a37f-1ce9618e2d4b" xlink:to="loc_us-gaap_EquityComponentDomain_019d0647-9fcc-7134-94e4-ac45c88fc0f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019d0647-9fcc-7eea-85c2-6aa899919342" 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_019d0647-9fcc-7134-94e4-ac45c88fc0f4" xlink:to="loc_us-gaap_CommonStockMember_019d0647-9fcc-7eea-85c2-6aa899919342" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019d0647-9fcc-773f-9fee-fcc8d1592b1d" 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_019d0647-9fcc-7134-94e4-ac45c88fc0f4" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019d0647-9fcc-773f-9fee-fcc8d1592b1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019d0647-9fcc-7dec-af63-da4abf08fdd9" 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_019d0647-9fcc-7134-94e4-ac45c88fc0f4" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019d0647-9fcc-7dec-af63-da4abf08fdd9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019d0647-9fcc-7375-8b6f-de582cb59c1a" 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_019d0647-9fcc-7134-94e4-ac45c88fc0f4" xlink:to="loc_us-gaap_RetainedEarningsMember_019d0647-9fcc-7375-8b6f-de582cb59c1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d0647-9fcc-7c86-9bf0-852d67bd77d6" 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_AccumulatedOtherComprehensiveIncomeLossLineItems_019d0647-9fcc-7883-8cd9-1ed2d46657a3" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019d0647-9fcc-79bc-9bd2-86b6bc773dcc" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_SharesOutstanding_019d0647-9fcc-79bc-9bd2-86b6bc773dcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019d0647-9fcc-73c7-ba46-d9b990734257" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_StockholdersEquity_019d0647-9fcc-73c7-ba46-d9b990734257" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019d0647-9fcc-7b13-b78b-fa2c3a972d6c" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019d0647-9fcc-7b13-b78b-fa2c3a972d6c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019d0647-9fcc-7ffe-a6a6-c8aa305b3497" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019d0647-9fcc-7ffe-a6a6-c8aa305b3497" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019d0647-9fcc-7675-8c45-a1ef9738c201" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019d0647-9fcc-7675-8c45-a1ef9738c201" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019d0647-9fcc-7ada-a2cb-24a5cbe9b552" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019d0647-9fcc-7ada-a2cb-24a5cbe9b552" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019d0647-9fcc-7d6b-a756-4fa04f0e9f04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019d0647-9fcc-7d6b-a756-4fa04f0e9f04" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d0647-9fcc-7eb2-a9d7-14a8b7bd7f11" 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_019d0647-9fcc-7c86-9bf0-852d67bd77d6" xlink:to="loc_us-gaap_NetIncomeLoss_019d0647-9fcc-7eb2-a9d7-14a8b7bd7f11" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019d0647-9fcc-7806-a6c3-7a74f785c20a" 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_019d0647-9fcc-7813-96a7-716550ef78e6" 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/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" 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_019d0647-9fcc-729f-94ec-907540f3ec81" 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_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d0647-9fcc-729f-94ec-907540f3ec81" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019db8a5-2c3e-7c14-82df-ae4b229825f1" 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_019d0647-9fcc-729f-94ec-907540f3ec81" xlink:to="loc_us-gaap_PlanNameAxis_019db8a5-2c3e-7c14-82df-ae4b229825f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019db8a5-2c3e-7c14-82df-ae4b229825f1_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_019db8a5-2c3e-7c14-82df-ae4b229825f1" xlink:to="loc_us-gaap_PlanNameDomain_019db8a5-2c3e-7c14-82df-ae4b229825f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019db8a5-2c3e-7317-96d9-90778d3e88d6" 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_019db8a5-2c3e-7c14-82df-ae4b229825f1" xlink:to="loc_us-gaap_PlanNameDomain_019db8a5-2c3e-7317-96d9-90778d3e88d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_InducementPlanMember_019db8a5-2c3e-7780-99db-cce5a32d9dd1" xlink:href="qtrx-20260331.xsd#qtrx_InducementPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019db8a5-2c3e-7317-96d9-90778d3e88d6" xlink:to="loc_qtrx_InducementPlanMember_019db8a5-2c3e-7780-99db-cce5a32d9dd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019db8a5-6693-730d-be73-c67f4359cc4b" 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_019d0647-9fcc-729f-94ec-907540f3ec81" xlink:to="loc_us-gaap_AwardTypeAxis_019db8a5-6693-730d-be73-c67f4359cc4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019db8a5-6693-730d-be73-c67f4359cc4b_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_019db8a5-6693-730d-be73-c67f4359cc4b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019db8a5-6693-730d-be73-c67f4359cc4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019db8a5-6693-7d1c-bcbb-3c39d5280b96" 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_019db8a5-6693-730d-be73-c67f4359cc4b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019db8a5-6693-7d1c-bcbb-3c39d5280b96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019db8a5-6693-7128-b4c1-a411bd26fca1" 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_019db8a5-6693-7d1c-bcbb-3c39d5280b96" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019db8a5-6693-7128-b4c1-a411bd26fca1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019db8a5-6693-77cb-bbf8-17d6d5f69918" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019db8a5-6693-7d1c-bcbb-3c39d5280b96" xlink:to="loc_us-gaap_PerformanceSharesMember_019db8a5-6693-77cb-bbf8-17d6d5f69918" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_PerformanceSharesMarketVestingConditionsMember_019df1cf-10cf-7019-ad19-3ea21ffa11e8" xlink:href="qtrx-20260331.xsd#qtrx_PerformanceSharesMarketVestingConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_019db8a5-6693-77cb-bbf8-17d6d5f69918" xlink:to="loc_qtrx_PerformanceSharesMarketVestingConditionsMember_019df1cf-10cf-7019-ad19-3ea21ffa11e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_PerformanceSharesPerformanceVestingConditionsMember_019df1d1-3c39-75c7-a270-218fb987f211" xlink:href="qtrx-20260331.xsd#qtrx_PerformanceSharesPerformanceVestingConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_019db8a5-6693-77cb-bbf8-17d6d5f69918" xlink:to="loc_qtrx_PerformanceSharesPerformanceVestingConditionsMember_019df1d1-3c39-75c7-a270-218fb987f211" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_RestrictedStockUnitsAndStockOptionsMember_019db8a5-7f5f-7473-9810-26562b56985b" xlink:href="qtrx-20260331.xsd#qtrx_RestrictedStockUnitsAndStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019db8a5-6693-7d1c-bcbb-3c39d5280b96" xlink:to="loc_qtrx_RestrictedStockUnitsAndStockOptionsMember_019db8a5-7f5f-7473-9810-26562b56985b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019df1c5-b5b7-7156-88ca-46ef875c8c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019df1c5-b5b7-7156-88ca-46ef875c8c0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019db8a5-2c3e-7ac8-a66c-2417c3f8c03c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019db8a5-2c3e-7ac8-a66c-2417c3f8c03c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumAwardPayout_019db8a5-6693-7798-bbe5-c9cacdb48c0c" xlink:href="qtrx-20260331.xsd#qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumAwardPayout"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_qtrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumAwardPayout_019db8a5-6693-7798-bbe5-c9cacdb48c0c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019db8a5-6693-70e8-8d7b-cef97503ff67" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019db8a5-6693-70e8-8d7b-cef97503ff67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019db8a5-6693-73bb-87f4-14a4c68f9e6a" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019db8a5-6693-73bb-87f4-14a4c68f9e6a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019de27f-eae6-7d59-9629-0f3b03e50cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019de27f-eae6-7d59-9629-0f3b03e50cdf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019db8a5-7f5f-7e74-8c3e-a3e4c4b3e992" 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_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019db8a5-7f5f-7e74-8c3e-a3e4c4b3e992" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019db8a5-7f5f-756a-a1f6-bfd9b6937343" 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_019db8a5-2c3e-77bc-a7b5-692b4dbed7d3" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019db8a5-7f5f-756a-a1f6-bfd9b6937343" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/StockBasedCompensationScheduleofSharebasedCompensationExpenseDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#StockBasedCompensationScheduleofSharebasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/StockBasedCompensationScheduleofSharebasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d0647-9fcc-7389-bfa9-a36d4d26fc74" 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_019d0647-9fcc-7f16-bd41-d46c8af119f5" 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_019d0647-9fcc-7389-bfa9-a36d4d26fc74" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d0647-9fcc-7f16-bd41-d46c8af119f5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019d0647-9fcc-786f-915f-6033e6c545dc" 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_019d0647-9fcc-7f16-bd41-d46c8af119f5" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019d0647-9fcc-786f-915f-6033e6c545dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019d0647-9fcc-786f-915f-6033e6c545dc_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_019d0647-9fcc-786f-915f-6033e6c545dc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019d0647-9fcc-786f-915f-6033e6c545dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019d0647-9fcc-7a64-883b-3b8a4fd83364" 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_019d0647-9fcc-786f-915f-6033e6c545dc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019d0647-9fcc-7a64-883b-3b8a4fd83364" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_CostOfProductRevenueMember_019d0647-9fcc-70a4-aac1-43a47150678f" xlink:href="qtrx-20260331.xsd#qtrx_CostOfProductRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d0647-9fcc-7a64-883b-3b8a4fd83364" xlink:to="loc_qtrx_CostOfProductRevenueMember_019d0647-9fcc-70a4-aac1-43a47150678f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9fcc-71fc-94e2-940f995ce6cf" xlink:href="qtrx-20260331.xsd#qtrx_ServiceAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d0647-9fcc-7a64-883b-3b8a4fd83364" xlink:to="loc_qtrx_ServiceAndOtherRevenueMember_019d0647-9fcc-71fc-94e2-940f995ce6cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019d0647-9fcc-725e-96a4-712cc29e5176" 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_019d0647-9fcc-7a64-883b-3b8a4fd83364" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019d0647-9fcc-725e-96a4-712cc29e5176" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019d0647-9fcc-75ae-84cc-f45a32d18509" 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_019d0647-9fcc-7a64-883b-3b8a4fd83364" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019d0647-9fcc-75ae-84cc-f45a32d18509" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019d0647-9fcc-7ef4-9ddd-a41b4acb9048" 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_019d0647-9fcc-7389-bfa9-a36d4d26fc74" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019d0647-9fcc-7ef4-9ddd-a41b4acb9048" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/NetLossPerShareScheduleofCommonShareEquivalentsExcludedfromDilutedNetLossPerShareDetails" xlink:type="simple" xlink:href="qtrx-20260331.xsd#NetLossPerShareScheduleofCommonShareEquivalentsExcludedfromDilutedNetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.quanterix.com/role/NetLossPerShareScheduleofCommonShareEquivalentsExcludedfromDilutedNetLossPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019d0647-9fcc-7574-98f4-70914a923915" 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_019d0647-9fcc-7744-91ec-91d05ddb4e52" 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_019d0647-9fcc-7574-98f4-70914a923915" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019d0647-9fcc-7744-91ec-91d05ddb4e52" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019d0647-9fcc-7938-8c7c-6e527514973f" 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_019d0647-9fcc-7744-91ec-91d05ddb4e52" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019d0647-9fcc-7938-8c7c-6e527514973f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019d0647-9fcc-7938-8c7c-6e527514973f_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_019d0647-9fcc-7938-8c7c-6e527514973f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019d0647-9fcc-7938-8c7c-6e527514973f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019d0647-9fcc-7a83-a1d0-b10d427e0b31" 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_019d0647-9fcc-7938-8c7c-6e527514973f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019d0647-9fcc-7a83-a1d0-b10d427e0b31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019d0647-9fcc-72f6-9244-fb1f9f9d2c15" 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_019d0647-9fcc-7a83-a1d0-b10d427e0b31" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019d0647-9fcc-72f6-9244-fb1f9f9d2c15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019d0647-9fcc-7b1d-865d-4b047d4d8bce" 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_019d0647-9fcc-7a83-a1d0-b10d427e0b31" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019d0647-9fcc-7b1d-865d-4b047d4d8bce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_EstimatedEsppPurchasesMember_019d0647-9fcc-7017-a4df-12b82919d1e0" xlink:href="qtrx-20260331.xsd#qtrx_EstimatedEsppPurchasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019d0647-9fcc-7a83-a1d0-b10d427e0b31" xlink:to="loc_qtrx_EstimatedEsppPurchasesMember_019d0647-9fcc-7017-a4df-12b82919d1e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019d0647-9fcc-768b-b401-4bb1b339050d" 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_019d0647-9fcc-7574-98f4-70914a923915" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019d0647-9fcc-768b-b401-4bb1b339050d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.quanterix.com/role/SegmentReportingScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="qtrx-20260331.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_019d0647-9fcc-7c4e-b795-6f0b15e88906" 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_019d0647-9fcc-7a30-ac57-4c14e01be66b" 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_019d0647-9fcc-7c4e-b795-6f0b15e88906" xlink:to="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_019d0647-9fcc-7a30-ac57-4c14e01be66b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d0647-9fcc-72d9-91d9-31d2ae00f0f9" 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_019d0647-9fcc-7a30-ac57-4c14e01be66b" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d0647-9fcc-72d9-91d9-31d2ae00f0f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d0647-9fcc-72d9-91d9-31d2ae00f0f9_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_019d0647-9fcc-72d9-91d9-31d2ae00f0f9" xlink:to="loc_us-gaap_SegmentDomain_019d0647-9fcc-72d9-91d9-31d2ae00f0f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d0647-9fcc-7fe5-8c77-a92732bce87f" 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_019d0647-9fcc-72d9-91d9-31d2ae00f0f9" xlink:to="loc_us-gaap_SegmentDomain_019d0647-9fcc-7fe5-8c77-a92732bce87f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_qtrx_ReportableSegmentMember_019d0647-9fcc-7ac3-9bee-bc77d7249ea5" xlink:href="qtrx-20260331.xsd#qtrx_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d0647-9fcc-7fe5-8c77-a92732bce87f" xlink:to="loc_qtrx_ReportableSegmentMember_019d0647-9fcc-7ac3-9bee-bc77d7249ea5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019d0647-9fcc-7d85-a04b-05b3895894be" 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_019d0647-9fcc-7c4e-b795-6f0b15e88906" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019d0647-9fcc-7d85-a04b-05b3895894be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019d0647-9fcc-702b-b8e7-cfeea0651604" 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_019d0647-9fcc-7c4e-b795-6f0b15e88906" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019d0647-9fcc-702b-b8e7-cfeea0651604" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_019d0647-9fcc-75d9-aae4-4d95c73fa3c6" 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_019d0647-9fcc-7c4e-b795-6f0b15e88906" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_019d0647-9fcc-75d9-aae4-4d95c73fa3c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019d0647-9fcc-7f19-baf3-5112c862e64f" 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_019d0647-9fcc-7c4e-b795-6f0b15e88906" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019d0647-9fcc-7f19-baf3-5112c862e64f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d0647-9fcc-7320-956e-8fe8dcd4c971" 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_019d0647-9fcc-7c4e-b795-6f0b15e88906" xlink:to="loc_us-gaap_NetIncomeLoss_019d0647-9fcc-7320-956e-8fe8dcd4c971" xlink:type="arc" order="4"/>
  </link:definitionLink>
</link:linkbase>
