UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

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Trinseo S.A.

(Name of Registrant as Specified In Its Charter)

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*** Exercise Your Right to Vote ***

Important Notice Regarding the Availability of Proxy Materials

for the Shareholder Meeting to Be Held on June 9, 2020.

Type:Annual General Meeting

 as of:April 20, 2020

June 9, 2020Time: 12:00 p.m. CEST

26-28, rue Edward Steichen

Meeting Information

Meeting Type:Annual General Meeting

For holders as of:April 20, 2020

Date:   June 9, 2020Time: 12:00 p.m. CEST

Location: 26-28, rue Edward Steichen

L-2540 Luxembourg

Grand Duchy of Luxembourg

You are receiving this communication because you hold shares in the company named above.

This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side).

We encourage you to access and review all of the important information contained in the proxy materials before voting.

See the reverse side of this notice to obtain proxy materials and voting instructions.

TRINSEO S.A.

TRINSEO S.A.

26-28, RUE EDWARD STEICHEN

L-2540 LUXEMBOURG

GRAND DUCHY OF LUXEMBOURG

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NOTICE AND PROXY STATEMENTANNUAL REPORT

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Voting Items The Board of Directors recommends you vote FOR the following proposals: 1.   To elect nine (9) Class II directors to serve for a term of one year expiring at the 2021 Annual General Meeting; Nominees: 1a.   Frank A. Bozich 1b.   K'Lynne Johnson 1c.   Sandra Beach Lin 1d.   Philip Martens 1e.   Donald T. Misheff 1f.   Christopher D. Pappas 1g.   Henri Steinmetz 1h.   Mark Tomkins 1i.   Stephen M. Zide 2.   To approve, on an advisory basis, the compensation paid by the Company to its named executive officers; 3.   To approve the Company’s annual accounts prepared in accordance with accounting principles generally accepted in Luxembourg for the year ended December 31, 2019 and its consolidated financial statements prepared in accordance with accounting principles generally accepted in the United States including a footnote reconciliation of equity and net income to International Financial Reporting Standards for the year ended December 31, 2019; 4.   To approve the allocation of the results of the year ended December 31, 2019; 5.   To approve the granting and discharge of the Company’s directors and auditor for the performance of their respective duties during the year ended December 31, 2019; 6.   To ratify the appointment of PricewaterhouseCoopers Société cooperative to be the Company’s independent auditor for all statutory accounts required by Luxembourg law for the year ending December 31, 2020; 7.   To ratify the appointment of PricewaterhouseCoopers LLP to be the Company’s independent registered public accounting firm for the year ending December 31, 2020; 8.   To approve, as required by Luxembourg law, an annual dividend in the amount of all interim dividends declared since the Company’s last Annual General Meeting of Shareholders; 9.   To approve the Company’s share repurchase authorization; and 10.   To approve an amendment to the Company’s Omnibus Incentive Plan. NOTE: Such other business as may properly come before the meeting or any adjournment thereof.