Exhibit 5.1

  May 21, 2019   ATTORNEYS AT LAW one independent drive, suite 1300 Jacksonville, Florida 32202-5017 904.359.2000 TEL 904.359.8700 FAX www.foley.com    

SeqLL Inc.

317 New Boston Street - Suite 210

Woburn, Massachusetts 01801

Re: Registration Statement on Form S-1

Ladies and Gentlemen:

We have acted as counsel to SeqLL Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) of the Company’s Registration Statement on Form S-1, File No. 333-230985 (as amended, and including any subsequent registration statement on Form S-1 filed pursuant to Rule 462(b), the “Registration Statement”), under the Securities Act of 1933, as amended (the “Act”), relating to the registration of the offer, issuance and sale by the Company of 1,552,500 shares of common stock, par value $0.00001 per share, which includes 202,500 shares to cover over-allotments, if any, (the “Shares”). The Shares are to be sold by the Company pursuant to an underwriting agreement among the Company and the Underwriters named therein (the “Underwriting Agreement”), the form of which is filed herewith as Exhibit 1.1 to the Registration Statement.

In so acting, we have examined originals or copies (certified or otherwise identified to our satisfaction) of (i) the form of Amended and Restated Certificate of Incorporation of the Company to be filed with the Secretary of State of the State of Delaware prior to the consummation of the initial public offering contemplated by the Registration Statement, filed as Exhibit 3.3 to the Registration Statement; (ii) the form of Amended and Restated Bylaws of the Company to be effective prior to the consummation of the initial public offering contemplated by the Registration Statement, filed as Exhibit 3.4 to the Registration Statement; (iii) the Registration Statement; (iv) the prospectus contained within the Registration Statement; (v) the form of the Underwriting Agreement and (vi) such corporate records, agreements, documents and other instruments, and such certificates or comparable documents of public officials and of officers and representatives of the Company, and have made inquiries of such officers and representatives, as we have deemed relevant and necessary as a basis for the opinion hereinafter set forth.

In such examination, we have assumed that the Amended and Restated Certificate of Incorporation that will be filed with the Secretary of State of the State of Delaware will be substantially identical to the form of Amended and Restated Certificate of Incorporation of the Company filed as Exhibit 3.3 to the Registration Statement, the genuineness of all signatures, the legal capacity of all natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, conformed or photostatic copies, and the authenticity of the originals of such latter documents. As to all questions of fact material to this opinion that have not been independently established, we have relied upon certificates or comparable documents of officers and representatives of the Company.

Boston Brussels CHICAGO Detroit JACKSONVILLE LOS ANGELES MADISON MIAMI MILWAUKEE NEW YORK ORLANDO SACRAMENTO SAN DIEGO SAN DIEGO/DEL MAR SAN FRANCISCO SHANGHAI SILICON VALLEY TALLAHASSEE TAMPA TOKYO WASHINGTON, D.C.

SeqLL Inc.

May 21, 2019

Page 2

Based on the foregoing, and subject to the qualifications stated herein, we are of the opinion that the Shares, when issued and sold as contemplated in the Registration Statement, and upon payment and delivery in accordance with the Underwriting Agreement, will be validly issued, fully paid and non-assessable.

The opinion expressed herein is limited to the General Corporation Law of the State of Delaware (including reported judicial decisions interpreting the General Corporation Law of the State of Delaware) and we express no opinion as to the effect on the matters covered by this letter of the laws of any other jurisdiction.

We hereby consent to the filing of this letter as an exhibit to the Registration Statement and to the reference to our firm under the caption “Legal Matters” in the prospectus which is a part of the Registration Statement. In giving such consents, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the Rules and Regulations of the Commission promulgated thereunder.

Sincerely,

/s/ FOLEY & LARDNER LLP