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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-05-10</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001703038</issuerCik>
        <issuerName>NRC GROUP HOLDINGS CORP.</issuerName>
        <issuerTradingSymbol>NRCG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755707</rptOwnerCik>
            <rptOwnerName>JFL-NRC-SES Partners, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755592</rptOwnerCik>
            <rptOwnerName>JFL AIV Investors III-JA, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755710</rptOwnerCik>
            <rptOwnerName>JFL-SES Int. (JA) Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755711</rptOwnerCik>
            <rptOwnerName>JFL-SES (JA) Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755708</rptOwnerCik>
            <rptOwnerName>JFL-SES Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755704</rptOwnerCik>
            <rptOwnerName>JFL-SES Partners, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755705</rptOwnerCik>
            <rptOwnerName>JFL-NRC Int. (JA) Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755709</rptOwnerCik>
            <rptOwnerName>JFL-NRC (JA) Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755706</rptOwnerCik>
            <rptOwnerName>JFL-NRC Partners, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755600</rptOwnerCik>
            <rptOwnerName>JFL GP Investors III, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O J.F. LEHMAN &amp; COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>110 EAST 59TH STREET, 27TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2019-05-10</value>
                <footnoteId id="F4"/>
                <footnoteId id="F5"/>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
                <footnoteId id="F5"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1147841</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.712</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>23021521</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>165568</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These securities of NRC Group Holdings Corp. (the &quot;Issuer&quot;) are held by JFL-NRC-SES Partners, LLC (&quot;JFL Partners&quot;). JFL Partners may be deemed to be controlled by its sole members, JFL-NRC Partners, LLC (&quot;JFL-NRC&quot;) and JFL-SES Partners, LLC (&quot;JFL-SES&quot;). JFL-SES is controlled by JFL-SES Holdings, LLC (&quot;SES Holdings&quot;), which is controlled by its member JFL-SES (JA) Holdings, LLC (&quot;JFL-SES (JA)&quot;), which is controlled by its sole member JFL-SES Int. (JA) Holdings, LLC (&quot;JFL-SES Int.&quot;), which is controlled by its member JFL AIV Investors III-JA, L.P. (&quot;JFL AIV&quot;). JFL-NRC is controlled by its member JFL-NRC (JA) Holdings, LLC (&quot;JFL-NRC (JA)&quot;), which is controlled by its sole member JFL-NRC Int. (JA) Holdings, LLC (&quot;JFL-NRC Int.&quot;), which is controlled by its member JFL AIV. JFL AIV is controlled by its general partner, JFL GP Investors III, LLC (&quot;Ultimate GP III&quot;). Ultimate GP III is controlled by its managers Messrs. John F. Lehman, Louis N. Mintz, Stephen L. Brooks, and C. Alexander Harman.</footnote>
        <footnote id="F2">These securities of the Issuer are held by JFL-NRCG Holdings III, LLC (&quot;JFL-NRCG III&quot;). JFL-NRCG III may be deemed to be controlled by its managing member, JFL-NRCG Annex Fund, LP (&quot;Annex Fund&quot;). Annex Fund is controlled by its general partner, Ultimate GP III. Ultimate GP III is controlled by its managers Messrs. Lehman, Mintz, Brooks, and Harman.</footnote>
        <footnote id="F3">Each of the Reporting Persons, and Messrs. Lehman, Mintz, Brooks and Harman, disclaims beneficial ownership of the securities reported herein or that may be beneficially owned by any of the other Reporting Persons, in each case except to the extent of any pecuniary interest therein, and this report shall not be deemed an admission that any such entity or person is the beneficial owner of or has any pecuniary interest in, such securities for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose.</footnote>
        <footnote id="F4">Pursuant to Sections 5.18(a) and 5.18(e) of the purchase agreement, dated June 25, 2018 and as amended on July 12, 2018 (the &quot;Purchase Agreement&quot;) pursuant to which the Issuer acquired all of the outstanding equity interests of NRC Group Holdings, LLC on October 17, 2018 (the &quot;Transaction&quot;), JFL Partners became entitled to a payment of $10.0 million (the &quot;Payment&quot;) on April 26, 2019, upon the consummation of the Potential Acquisition (as defined in the Purchase Agreement). Pursuant to the Purchase Agreement the Payment could be made in cash, common stock of the Issuer, or any combination thereof, at the Issuer's option. Following the consummation of the Potential Acquisition, on May 10, 2019, the Issuer's board (upon the election and recommendation of the disinterested directors not associated with entities affiliated with JFL-Partners) authorized</footnote>
        <footnote id="F5">(Continued from Footnote 4) the Payment be made entirely in common stock of the Issuer. The number of shares issuable under the Payment was determined pursuant to a formula set forth in the Purchase Agreement, which provided that the value of each share issued pursuant to the Payment was an amount equal to the volume-weighted average price per share of the Issuer's common stock on the NYSE American for the five consecutive trading days preceding (but not including) the closing of the Potential Acquisition (which in this case was April 26, 2019). Accordingly, the value of each share of common stock issued was $8.712, and the total number of shares being issued was 1,147,841. JFL Partners right to receive additional shares of common stock of the Issuer pursuant to the Payment became fixed and irrevocable on October 17, 2018, the effective date of the Transaction, subject only to consummation of the Potential Acquisition.</footnote>
    </footnotes>

    <remarks>Because no more than 10 reporting persons can file any one Form 4 through the Securities and Exchange Commission's EDGAR system, JFL-NRCG III and Annex Fund have filed a separate Form 4. The Reporting Persons are jointly filing this Form 4.</remarks>

    <ownerSignature>
        <signatureName>JFL GP Investors III, LLC., By: /s/ David Rattner, attorney-in-fact</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL AIV Investors III-JA, L.P., By: JFL GP Investors III, LLC, Its General PartnerBy: /s/ David Rattner, attorney-in-fact</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-SES Int. (JA) Holdings, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-SES (JA) Holdings, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-SES Holdings, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-SES Partners, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-NRC Int. (JA) Holdings, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-NRC (JA) Holdings, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-NRC Partners, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>JFL-NRC-SES Partners, LLC., By: /s/ David Rattner, as secretary</signatureName>
        <signatureDate>2019-05-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
