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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-10-21</periodOfReport>

    <issuer>
        <issuerCik>0001373561</issuerCik>
        <issuerName>NewStar Financial, Inc.</issuerName>
        <issuerTradingSymbol>NEWS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001419137</rptOwnerCik>
            <rptOwnerName>Capital Z Partners III GP, Ltd.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001455704</rptOwnerCik>
            <rptOwnerName>Capital Z Partners Management, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001419144</rptOwnerCik>
            <rptOwnerName>Capital Z Partners III, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001308745</rptOwnerCik>
            <rptOwnerName>CAPITAL Z FINANCIAL SERVICES PRIVATE FUND II, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001075567</rptOwnerCik>
            <rptOwnerName>CAPITAL Z FINANCIAL SERVICES FUND II LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001075560</rptOwnerCik>
            <rptOwnerName>CAPITAL Z PARTNERS LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001075558</rptOwnerCik>
            <rptOwnerName>CAPITAL Z PARTNERS LTD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001008262</rptOwnerCik>
            <rptOwnerName>COOPER BRADLEY E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>true</isDirector>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001419136</rptOwnerCik>
            <rptOwnerName>Capital Z Partners III GP, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>142 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-10-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1989402</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.93</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3528286</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-10-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10598</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.93</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18805</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28970</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4000000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29919</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Disposition transactions made pursuant to a privately-negotiated repurchase agreement, which transactions are scheduled to close on or before October 28, 2016.</footnote>
        <footnote id="F2">Represents securities held directly by Capital Z Financial Services Fund II, L.P. (&quot;Capital Z Fund&quot;).</footnote>
        <footnote id="F3">The sole general partner of Capital Z Fund and Capital Z Financial Services Private Fund II, L.P. (&quot;Capital Z Private Fund&quot;) is Capital Z Partners, L.P. (&quot;Capital Z GP LP&quot;), whose sole general partner is Capital Z Partners, Ltd. (&quot;Capital Z GP LTD&quot;).  Capital Z Partners Management, LLC (&quot;CZPM&quot;) performs investment management services for Capital Z Fund and Capital Z Private Fund.  By reason of the provisions of Rule 16a-1 of the Exchange Act, Capital Z GP LP, Capital Z GP LTD and CZPM may be deemed to be the beneficial owners of the securities held by Capital Z Fund and Capital Z Private Fund, but each individual entity described above disclaims beneficial ownership of securities held by any other entity except to the extent of any indirect pecuniary interest therein.</footnote>
        <footnote id="F4">Represents securities held directly by Capital Z Private Fund.</footnote>
        <footnote id="F5">Represents securities held directly by CZPM.</footnote>
        <footnote id="F6">Represents securities held directly by Capital Z Partners III, L.P. (&quot;Capital Z III Fund&quot;). The sole general partner of Capital Z III Fund is Capital Z Partners III GP, L.P. (&quot;Capital Z III GP LP&quot;), whose sole general partner is Capital Z Partners III GP, Ltd. (&quot;Capital Z III GP LTD&quot;).  CZPM performs investment management services for Capital Z III Fund.  By reason of the provisions of Rule 16a-1 of the Exchange Act, Capital Z III GP LP, Capital Z III LP LTD and CZPM may be deemed to be the beneficial owners of the securities held by Capital Z III Fund, but each individual entity described above disclaims beneficial ownership of securities held by any other entity except to the extent of any indirect pecuniary interest therein.</footnote>
        <footnote id="F7">Directly owned by Bradley E. Cooper.  Bradley E. Cooper is a limited partner of both Capital Z III GP LP and Capital Z GP LP, and he is an officer and co-owner of CZPM.  Mr. Cooper disclaims beneficial ownership of securities beneficially owned by them, except to the extent of any pecuniary interest therein.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Partners III GP, Ltd.</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Partners Management, LLC</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Partners III, L.P</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Financial Services Private Fund II, L.P.</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Financial Services Fund II, L.P.</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Partners, L.P.</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Partners, Ltd.</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Bradley E. Cooper</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Craig Fisher, Authorized Signatory for Capital Z Partners III GP, L.P.</signatureName>
        <signatureDate>2016-10-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
