<?xml version="1.0"?>
<edgarSubmission>

    <schemaVersion>X0708</schemaVersion>

    <submissionType>D</submissionType>

    <testOrLive>LIVE</testOrLive>

    <primaryIssuer>
        <cik>0001925531</cik>
        <entityName>New Mountain Guardian IV BDC L.L.C.</entityName>
        <issuerAddress>
            <street1>1633 BROADWAY</street1>
            <street2>48TH FLOOR</street2>
            <city>NEW YORK</city>
            <stateOrCountry>NY</stateOrCountry>
            <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
            <zipCode>10019</zipCode>
        </issuerAddress>
        <issuerPhoneNumber>212-720-0300</issuerPhoneNumber>
        <jurisdictionOfInc>DELAWARE</jurisdictionOfInc>
        <issuerPreviousNameList>
            <value>None</value>
        </issuerPreviousNameList>
        <edgarPreviousNameList>
            <value>None</value>
        </edgarPreviousNameList>
        <entityType>Limited Liability Company</entityType>
        <yearOfInc>
            <withinFiveYears>true</withinFiveYears>
            <value>2022</value>
        </yearOfInc>
    </primaryIssuer>

    <relatedPersonsList>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>N/A</firstName>
                <lastName>New Mountain Finance Advisers BDC, L.L.C.</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Promoter</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Adam</firstName>
                <lastName>Weinstein</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Director, Executive Vice President</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>John</firstName>
                <middleName>R.</middleName>
                <lastName>Kline</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Director, President</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Alfred</firstName>
                <middleName>F.</middleName>
                <lastName>Hurley, Jr.</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Rome</firstName>
                <middleName>G.</middleName>
                <lastName>Arnold III</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>David</firstName>
                <lastName>Ogens</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Robert</firstName>
                <middleName>A.</middleName>
                <lastName>Hamwee</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Chief Executive Officer</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Joseph</firstName>
                <lastName>Hartswell</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>CCO and Corporate Secretary</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Shiraz</firstName>
                <middleName>Y.</middleName>
                <lastName>Kajee</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Chief Financial Officer and Treasurer</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Laura</firstName>
                <lastName>Holson</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>1633 Broadway, 48th Floor</street1>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10019</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>Chief Operating Officer</relationshipClarification>
        </relatedPersonInfo>
    </relatedPersonsList>

    <offeringData>
        <industryGroup>
            <industryGroupType>Pooled Investment Fund</industryGroupType>
            <investmentFundInfo>
                <investmentFundType>Other Investment Fund</investmentFundType>
                <is40Act>false</is40Act>
            </investmentFundInfo>
        </industryGroup>
        <issuerSize>
            <aggregateNetAssetValueRange>Decline to Disclose</aggregateNetAssetValueRange>
        </issuerSize>
        <federalExemptionsExclusions>
            <item>06b</item>
        </federalExemptionsExclusions>
        <typeOfFiling>
            <newOrAmendment>
                <isAmendment>false</isAmendment>
            </newOrAmendment>
            <dateOfFirstSale>
                <yetToOccur>true</yetToOccur>
            </dateOfFirstSale>
        </typeOfFiling>
        <durationOfOffering>
            <moreThanOneYear>true</moreThanOneYear>
        </durationOfOffering>
        <typesOfSecuritiesOffered>
            <isEquityType>true</isEquityType>
        </typesOfSecuritiesOffered>
        <businessCombinationTransaction>
            <isBusinessCombinationTransaction>false</isBusinessCombinationTransaction>
            <clarificationOfResponse></clarificationOfResponse>
        </businessCombinationTransaction>
        <minimumInvestmentAccepted>0</minimumInvestmentAccepted>
        <salesCompensationList>
            <recipient>
                <recipientName>Acro Securities</recipientName>
                <recipientCRDNumber>None</recipientCRDNumber>
                <associatedBDName>None</associatedBDName>
                <associatedBDCRDNumber>None</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>Skolavoroustigur 25</street1>
                    <city>101 Reykjavik</city>
                    <stateOrCountry>K6</stateOrCountry>
                    <stateOrCountryDescription>ICELAND</stateOrCountryDescription>
                    <zipCode>-</zipCode>
                </recipientAddress>
                <statesOfSolicitationList></statesOfSolicitationList>
                <foreignSolicitation>true</foreignSolicitation>
            </recipient>
            <recipient>
                <recipientName>Ameris Capital Limitada</recipientName>
                <recipientCRDNumber>None</recipientCRDNumber>
                <associatedBDName>None</associatedBDName>
                <associatedBDCRDNumber>None</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>Av. El Golf 82</street1>
                    <street2>Piso 5</street2>
                    <city>Santiago</city>
                    <stateOrCountry>F3</stateOrCountry>
                    <stateOrCountryDescription>CHILE</stateOrCountryDescription>
                    <zipCode>-</zipCode>
                </recipientAddress>
                <statesOfSolicitationList></statesOfSolicitationList>
                <foreignSolicitation>true</foreignSolicitation>
            </recipient>
            <recipient>
                <recipientName>TransPacific Group LLC</recipientName>
                <recipientCRDNumber>143869</recipientCRDNumber>
                <associatedBDName>TransPacific Group LLC</associatedBDName>
                <associatedBDCRDNumber>143869</associatedBDCRDNumber>
                <recipientAddress>
                    <street1>150 SE 2nd Avenue</street1>
                    <city>Miami</city>
                    <stateOrCountry>FL</stateOrCountry>
                    <stateOrCountryDescription>FLORIDA</stateOrCountryDescription>
                    <zipCode>33131</zipCode>
                </recipientAddress>
                <statesOfSolicitationList>
                    <state>FL</state>
                    <description>FLORIDA</description>
                    <state>NY</state>
                    <description>NEW YORK</description>
                </statesOfSolicitationList>
                <foreignSolicitation>false</foreignSolicitation>
            </recipient>
        </salesCompensationList>
        <offeringSalesAmounts>
            <totalOfferingAmount>Indefinite</totalOfferingAmount>
            <totalAmountSold>0</totalAmountSold>
            <totalRemaining>Indefinite</totalRemaining>
            <clarificationOfResponse></clarificationOfResponse>
        </offeringSalesAmounts>
        <investors>
            <hasNonAccreditedInvestors>false</hasNonAccreditedInvestors>
            <totalNumberAlreadyInvested>0</totalNumberAlreadyInvested>
        </investors>
        <salesCommissionsFindersFees>
            <salesCommissions>
                <dollarAmount>1000000</dollarAmount>
                <isEstimate>true</isEstimate>
            </salesCommissions>
            <findersFees>
                <dollarAmount>0</dollarAmount>
            </findersFees>
            <clarificationOfResponse></clarificationOfResponse>
        </salesCommissionsFindersFees>
        <useOfProceeds>
            <grossProceedsUsed>
                <dollarAmount>0</dollarAmount>
            </grossProceedsUsed>
            <clarificationOfResponse></clarificationOfResponse>
        </useOfProceeds>
        <signatureBlock>
            <authorizedRepresentative>false</authorizedRepresentative>
            <signature>
                <issuerName>New Mountain Guardian IV BDC L.L.C.</issuerName>
                <signatureName>/s/ Adam B. Weinstein</signatureName>
                <nameOfSigner>Adam B. Weinstein</nameOfSigner>
                <signatureTitle>Director, Executive Vice President</signatureTitle>
                <signatureDate>2022-05-03</signatureDate>
            </signature>
        </signatureBlock>
    </offeringData>
</edgarSubmission>
