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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2019-11-12T21:10:06.6562551+00:00 -->
<!-- Version            : 5.0.0.208 -->
<!-- Package ID         : 5daebc71125e4c4783e9ea9bc67b0f18 -->
<!-- Copyright (c) 2019 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="ngm_CollaborativeAgreementConsiderationMilestone" name="CollaborativeAgreementConsiderationMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_ReceivedAmountFromOptions" name="ReceivedAmountFromOptions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_ReductionInPercentageOfSecuritiesOwnedByRelatedPartyUponEarlyCompletionOfResearchTerm" name="ReductionInPercentageOfSecuritiesOwnedByRelatedPartyUponEarlyCompletionOfResearchTerm" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_EligibleToReceiveOneTimePaymentForOptionedProgram" name="EligibleToReceiveOneTimePaymentForOptionedProgram" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_EligibleMilestonePaymentsReceivable" name="EligibleMilestonePaymentsReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_EligibleMilestonePaymentReceivableUponPotentialAchievementOfSpecificClinicalDevelopmentEvents" name="EligibleMilestonePaymentReceivableUponPotentialAchievementOfSpecificClinicalDevelopmentEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_EligibleMilestonePaymentReceivableUponPotentialAchievementOfCertainRegulatoryEvents" name="EligibleMilestonePaymentReceivableUponPotentialAchievementOfCertainRegulatoryEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_MilestonePaymentForPotentialAchievementOfCertainClinicalDevelopmentEvents" name="MilestonePaymentForPotentialAchievementOfCertainClinicalDevelopmentEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_ResearchCollaborationAndLicenseAgreementsAbstract" name="ResearchCollaborationAndLicenseAgreementsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_FirstIndicationMember" name="FirstIndicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SecondIndicationMember" name="SecondIndicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ThirdIndicationMember" name="ThirdIndicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ClinicalTrialToFirstPatientInFirstPhaseThreeMember" name="ClinicalTrialToFirstPatientInFirstPhaseThreeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_MilestonePaymentForPotentialAchievementOfCertainRegulatoryEvents" name="MilestonePaymentForPotentialAchievementOfCertainRegulatoryEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_DisclosureResearchCollaborationAndLicenseAgreementsScheduleOfRecognizedRevenueFromCollaborationAndLicenseAgreementsDetailsAbstract" name="DisclosureResearchCollaborationAndLicenseAgreementsScheduleOfRecognizedRevenueFromCollaborationAndLicenseAgreementsDetailsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_UpfrontLicenseFee" name="UpfrontLicenseFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_EligibleToReceiveCommercialMilestonePaymentsForEachLicensedProduct" name="EligibleToReceiveCommercialMilestonePaymentsForEachLicensedProduct" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_AmortizationOfUpfrontLicenseFee" name="AmortizationOfUpfrontLicenseFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_ContractWithCustomerLiabilityPeriodIncreaseDecrease" name="ContractWithCustomerLiabilityPeriodIncreaseDecrease" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_OperatingLeaseAgreementAmendmentPeriod" name="OperatingLeaseAgreementAmendmentPeriod" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_OperatingLeaseExpirationPeriod" name="OperatingLeaseExpirationPeriod" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_CommitmentsAndContingenciesDisclosureLineItems" name="CommitmentsAndContingenciesDisclosureLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommitmentsAndContingenciesDisclosureTable" name="CommitmentsAndContingenciesDisclosureTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CorporateOfficeSpaceAndLaboratoryFacilityMember" name="CorporateOfficeSpaceAndLaboratoryFacilityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ReductionInSecurityDeposit" name="ReductionInSecurityDeposit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_RemainingOperatingLeasePaymentsFromRelatedPartyToLessor" name="RemainingOperatingLeasePaymentsFromRelatedPartyToLessor" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_SeriesAConvertiblePreferredStockMember" name="SeriesAConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SeriesBConvertiblePreferredStockMember" name="SeriesBConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SeriesCConvertiblePreferredStockMember" name="SeriesCConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SeriesDConvertiblePreferredStockMember" name="SeriesDConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SeriesABCDAndEConvertiblePreferredStockMember" name="SeriesABCDAndEConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_StockOptionFiscalTwentyEighteenPlanMember" name="StockOptionFiscalTwentyEighteenPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_TenPercentOrGreaterStockholderMember" name="TenPercentOrGreaterStockholderMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_EmployeesAndDirectorsMember" name="EmployeesAndDirectorsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommonStockOptionsOutstandingMember" name="CommonStockOptionsOutstandingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommonStockOptionsAvailableForGrantMember" name="CommonStockOptionsAvailableForGrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_FourZeroOneKMatchingPlanMember" name="FourZeroOneKMatchingPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantsInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantsInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantExercisedInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantExercisedInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeituresInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeituresInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_SharesRightToRepurchaseLapsePeriod" name="SharesRightToRepurchaseLapsePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareRepurchaseProgramRepurchasePricePerShare" name="ShareRepurchaseProgramRepurchasePricePerShare" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ngm_EarlyExerciseOfStockOptionLiabilities" name="EarlyExerciseOfStockOptionLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureRate" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureRate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_EmployeesMember" name="EmployeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_OfferingPeriodForPurchaseUnderEmployeeStockPurchasePlan" name="OfferingPeriodForPurchaseUnderEmployeeStockPurchasePlan" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_NumberOfPurchasePeriods" name="NumberOfPurchasePeriods" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_DurationOfEachPurchasePeriod" name="DurationOfEachPurchasePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
