Syneos Health, Inc. Lock-Up Agreement August 6, 2018

Exhibit 99.3

Syneos Health, Inc.

Lock-Up Agreement

August 6, 2018

▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. LLC

▇▇▇▇ ▇▇▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Re: Syneos Health, Inc. - Lock-Up Agreement

Ladies and Gentlemen:

The undersigned understands that you, propose to enter into an Underwriting Agreement (collectively, the “Underwriters”), with Syneos Health, Inc., a Delaware corporation (the “Company”), and the Selling Stockholders named in Schedule II to such agreement providing for a public offering of shares of Class A Common Stock, par value $0.01 (the “Stock”) of the Company (the “Shares”) pursuant to the Registration Statement on Form S-3 (No. 333-208286) filed with the Securities and Exchange Commission (the “SEC”).

In consideration of the agreement by the Underwriters to offer and sell the Shares, and of other good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the undersigned agrees that, during the period specified in the following paragraph (the “Stockholder Lock-Up Period”), the undersigned will not offer, sell, contract to sell, pledge, grant any option to purchase, make any short sale or otherwise dispose of any shares of Stock of the Company, or any options or warrants to purchase any shares of Stock of the Company, or any securities convertible into, exchangeable for or that represent the right to receive shares of Stock of the Company, whether now owned or hereinafter acquired, owned directly by the undersigned (including holding as a custodian) or with respect to which the undersigned has beneficial ownership within the rules and regulations of the SEC (collectively the “Undersigned’s Shares”).  The foregoing restriction is expressly agreed to preclude the undersigned from engaging in any hedging or other transaction which is designed to or which reasonably could be expected to lead to or result in a sale or disposition of the Undersigned’s Shares even if such Shares would be disposed of by someone other than the undersigned.  Such prohibited hedging or other transactions would include without limitation any short sale or any purchase, sale or grant of any right (including without limitation any put or call option) with respect to any of the Undersigned’s Shares or with respect to any security that includes, relates to, or derives any significant part of its value from such Shares.

The Stockholder Lock-Up Period will commence on the date of this Lock-Up Agreement and continue for 30 days after the public offering date set forth on the final prospectus used to sell the Shares pursuant to the Underwriting Agreement.

Notwithstanding the foregoing, the undersigned may transfer the Undersigned’s Shares:

(i) as a bona fide gift or gifts;

(ii) to any beneficiary of the undersigned pursuant to a will, other testamentary document or intestate succession to the legal representatives, heirs, beneficiary or immediate family member of the undersigned;

(iii) to any trust, partnership, limited liability company or other entity for the direct or indirect benefit of the undersigned or the immediate family of the undersigned;

(iv) to any immediate family member or other dependent;

(v) as a distribution to limited partners, members or stockholders of the undersigned;

(vi) to the undersigned’s affiliates or to any investment fund or other entity controlled or managed by the undersigned;

(vii) to a nominee or custodian of a person or entity to whom a disposition or transfer would be permissible under clauses (i) through (vi) above;

(viii) pursuant to an order of a court or regulatory agency or to comply with any regulations related to the Undersigned’s ownership of Shares; provided that in the case of any transfer or distribution pursuant this clause, any filing under Section 16(a) of the Exchange Act, reporting a reduction in beneficial ownership of shares of Stock, shall state that such transfer is pursuant to an order of a court or regulatory agency or to comply with any regulations related to the ownership of the Shares unless such a statement would be prohibited by any applicable law, regulation or order of a court or regulatory agency;

(ix) to the Company or its affiliates upon death, disability or termination of employment, in each case, of the Undersigned;

(x) to the Company or its affiliates (A) deemed to occur upon the cashless exercise of options or (B) for the primary purpose of paying the exercise price of such options or for paying taxes (including estimated taxes) due as a result of the exercise of such options or as a result of the vesting of Stock under restricted stock units or restricted stock awards, in each case pursuant to employee benefit plans disclosed in the Registration Statement; provided that in the case of any transfer or distribution pursuant this clause, except as a result of the vesting of Stock under restricted stock units or restricted stock awards, no filing under Section 16(a) of the Exchange Act (other than a filing on Form 5), reporting a reduction in beneficial ownership of shares of Stock, shall be required or shall be voluntarily made during the Stockholder Lock-Up Period;

(xi) in connection with transactions by any person other than the Company relating to Shares acquired in open market transactions after the completion of the Offering;

(xii) pursuant to a bona fide third party tender offer, merger, consolidation, stock exchange or similar transaction that is approved by the Board of Directors of the Company and made to all holders of the Stock involving a Change of Control (as defined below) of the Company; provided, that if any such tender offer, merger, consolidation, stock exchange or similar transaction is not consummated, such Lock-Up Securities shall remain subject to this agreement; or

(xiii) with the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. LLC.

provided that, (1) in the case of each transfer or distribution pursuant to clauses (i) through (vii) above, each donee, trustee, distributee or transferee, as the case may be, agrees to be bound in writing by the restrictions set forth herein, (2) in the case of each transfer or distribution pursuant to clauses (v) through (vii) above, shall not involve a disposition for value and (3) in the case of each transfer or distribution pursuance to clauses (i), (iii) through (vi) and (xi) above, no filing under Section 16(a) of the Exchange Act (other than a filing on Form 5) reporting a reduction in beneficial ownership of shares of Stock, shall be required or shall be voluntarily made during the Lock-Up Period. For purposes of this Lock-Up Agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not more remote than first cousin.

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For purposes of this Lock-Up Agreement, “Change of Control” shall mean the transfer (whether by tender offer, merger, consolidation or other similar transaction), in one transaction or a series of related transactions, to a person or group of affiliated persons, of the voting power of the Company’s capital stock if, after such transfer, such person or group of affiliated persons would hold more than 50% of the outstanding voting power of the Company’s capital stock (or of the surviving entity).

In addition, notwithstanding the foregoing, if the undersigned is a corporation, the corporation may transfer the capital stock of the Company to any wholly-owned subsidiary of such corporation; provided, however, that in any such case, it shall be a condition to the transfer that the transferee execute an agreement stating that the transferee is receiving and holding such capital stock subject to the provisions of this Agreement and there shall be no further transfer of such capital stock except in accordance with this Agreement, and provided further that any such transfer shall not involve a disposition for value.  The undersigned now has, and, except as contemplated by clauses (i) through (xiii) above, for the duration of this Lock-Up Agreement will have, good and marketable title to the Undersigned’s Shares, free and clear of all liens, encumbrances, and claims whatsoever.  The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of the Undersigned’s Shares except in compliance with the foregoing restrictions.

The restrictions described in this Lock-Up Agreement shall not apply to: (a) the sale of the Undersigned’s Shares pursuant to the Underwriting Agreement; (b) any transactions effectuated pursuant to a trading plan that satisfies all of the requirements of Rule 10b5-1 under the Exchange Act (“10b5-1 Plan”) existing on the date hereof; or (c) the establishment of a 10b5-1 Plan, provided that no transfers occur under such plan during such Lock-Up Period and no public announcement or filing shall be required or voluntarily made by any person in connection therewith until after the expiration of the Lock-Up Period.

This Lock-Up Agreement shall be terminated and the undersigned shall be released from its obligations hereunder upon the earlier of (i) the date the Registration Statement filed with the SEC with respect to the offering is withdrawn, (ii) the date on which for any reason the Underwriting Agreement is terminated (other than the provisions thereof that survive termination) prior to payment for and delivery of the Shares to be sold thereunder or (iii) August 31, 2018, if the Offering is not completed by such date.

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The undersigned understands that the Company and the Underwriters are relying upon this Lock-Up Agreement in proceeding toward consummation of the offering.  The undersigned further understands that this Lock-Up Agreement is irrevocable and shall be binding upon the undersigned’s heirs, legal representatives, successors, and assigns.

	Very truly yours,
	▇▇▇▇▇▇ ▇. ▇▇▇ EQUITY FUND VI, L.P.
	By:  THL Equity Advisors VI, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	▇▇▇▇▇▇ ▇. ▇▇▇ PARALLEL FUND VI, L.P.
	By:  THL Equity Advisors VI, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	▇▇▇▇▇▇ ▇. ▇▇▇ PARALLEL (DT) FUND VI, L.P.
	By:  THL Equity Advisors VI, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

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	GREAT-WEST INVESTORS, LP
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its attorney-in-fact
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	▇▇▇▇▇▇ INVESTMENTS EMPLOYEES’ SECURITIES COMPANY III, LLC
	By:  ▇▇▇▇▇▇ Investment Holdings, LLC, its managing member
	By:  ▇▇▇▇▇▇ Investments, LLC, its managing member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its attorney-in-fact
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	THL COINVESTMENT PARTNERS, L.P.
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	THL OPERATING PARTNERS, L.P.
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

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	▇▇▇▇▇▇ ▇. ▇▇▇ EQUITY FUND VII, L.P.
	By:  THL Equity Advisors VII, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	▇▇▇▇▇▇ ▇. ▇▇▇ PARALLEL FUND VII, L.P.
	By:  THL Equity Advisors VII, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	▇▇▇▇▇▇ ▇. ▇▇▇ PARALLEL (CAYMAN) FUND VII, L.P.
	By:  THL Equity Advisors VII, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	THL EXECUTIVE FUND VII, L.P.
	By:  THL Equity Advisors VII, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

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	THL FUND VII COINVESTMENT PARTNERS, L.P.
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

	THL EQUITY FUND VII INVESTORS (INVENTIV), L.P.
	By:  THL Equity Advisors VII, LLC, its general partner
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Partners, L.P., its sole member
	By:  ▇▇▇▇▇▇ ▇. ▇▇▇ Advisors, LLC, its general partner
	By:  THL Holdco, LLC, its managing member
	By:	/s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
		Title:    Managing Director

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