JOINT FILING AGREEMENT PURSUANT TO RULE 13d-1(k)(1)

Exhibit 99.19

JOINT FILING AGREEMENT PURSUANT TO RULE 13d-1(k)(1)

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing on behalf of each of them of the Schedule 13D to which this Agreement is an exhibit (and any further amendment filed by them) with respect to the shares of Class A Common Stock of Syneos Health, Inc. This agreement may be executed simultaneously in any number of counterparts, all of which together shall constitute one and the same instrument.

Dated: June 9, 2021

	XXXXXX X. XXX ADVISORS, LLC
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL HOLDCO, LLC
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	XXXXXX X. XXX PARTNERS, L.P.
	By: Xxxxxx X. Xxx Advisors, LLC, its General Partner
	By: THL Holdco, LLC, its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL EQUITY ADVISORS VI (2019), LLC
	By: Xxxxxx X. Xxx Partners, L.P.,
	its Sole Member
	By: Xxxxxx X. Xxx Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company

1

	XXXXXX X. XXX EQUITY FUND VI (2019), L.P.
	By: THL Equity Advisors VI (2019), LLC,
	its General Partner
	By: Xxxxxx X. Xxx Partners, L.P.,
	its Sole Member
	By: Xxxxxx X. Xxx Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL EQUITY FUND VI (2019) COINVESTMENT PARTNERS, L.P.
	By: Xxxxxx X. Xxx Partners, L.P.,
	its General Partner
	By: Xxxxxx X. Xxx Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL EQUITY ADVISORS VII, LLC
	By: Xxxxxx X. Xxx Partners, L.P.,
	its Sole Member
	By: Xxxxxx X. Xxx Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL FUND VII COINVESTMENT PARTNERS, L.P.
	By: Xxxxxx X. Xxx Partners, L.P.,
	its General Partner
	By: Xxxxxx X. Xxx Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company

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	THL EQUITY FUND VII INVESTORS (INVENTIV), L.P.
	XXXXXX X. XXX EQUITY FUND VII, L.P.
	XXXXXX X. XXX PARALLEL FUND VII, L.P.
	XXXXXX X. XXX PARALLEL (CAYMAN) FUND VII, L.P.
	THL EXECUTIVE FUND VII, L.P.
	By: THL Equity Advisors VII, LLC,
	its General Partner
	By: Xxxxxx X. Xxx Partners, L.P.,
	its Sole Member
	By: Xxxxxx X. Xxx Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL MANAGERS VI, LLC
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company
	THL MANAGERS VII, LLC
	By:	/s/Xxxxxxx XxXxxxxxx
	Name: Xxxxxxx XxXxxxxxx
	Title: Chief Financial Officer, Management Company

3