Exhibit 5.1

Hogan Lovells US LLP Columbia Square 555 Thirteenth Street, NW Washington, DC 20004 T +1 202 637 5600 F +1 202 637 5910 www.hoganlovells.com

November 25, 2020

Board of Directors

Griffin Capital Essential Asset REIT, Inc.

1520 E. Grand Avenue

El Segundo, CA 90245

Ladies and Gentlemen:

We are acting as counsel to Griffin Capital Essential Asset REIT, Inc., a Maryland corporation (the “Company”), in connection with its registration statement on Form S-4, as amended (the “Registration Statement”), filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Act”) relating to the proposed public offering of up to 93,457,668 shares of the common stock, par value $0.001 per share, of the Company (the “Shares”), in connection with the mergers contemplated by the Agreement and Plan of Merger, dated as of October 29, 2020 (the “Merger Agreement”), by and among (i) the Company, (ii) GRT (Cardinal REIT Merger Sub), LLC, a Maryland limited liability company and a wholly owned subsidiary of the Company, (iii) Griffin Capital Essential Asset Operating Partnership, L.P., a Delaware limited partnership and a subsidiary of the Company (the “GCEAR Operating Partnership”), (iv) GRT OP (Cardinal New GP Sub), LLC, a Delaware limited liability company and a wholly owned subsidiary of the GCEAR Operating Partnership (“New GP Sub”), (v) GRT OP (Cardinal LP Merger Sub), LLC, a Delaware limited liability company and a wholly owned subsidiary of the GCEAR Operating Partnership (“LP Merger Sub”), (vi) GRT OP (Cardinal OP Merger Sub), LLC, a Delaware limited liability company and a subsidiary of LP Merger Sub and New GP Sub, (vii) Cole Office & Industrial REIT (CCIT II), Inc., a Maryland corporation (“CCIT II”), (viii) Cole Corporate Income Operating Partnership II, LP, a Delaware limited partnership and a wholly owned subsidiary of CCIT II, and (ix) CRI CCIT II LLC, a Delaware limited liability company and a wholly owned subsidiary of CCIT II. This opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement.

For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the conformity to authentic

Hogan Lovells US LLP is a limited liability partnership registered in the District of Columbia. “Hogan Lovells” is an international legal practice that includes Hogan Lovells US LLP and Hogan Lovells International LLP, with offices in: Alicante Amsterdam Baltimore Beijing Birmingham Boston Brussels Colorado Springs Denver Dubai Dusseldorf Frankfurt Hamburg Hanoi Ho Chi Minh City Hong Kong Houston Johannesburg London Los Angeles Luxembourg Madrid Mexico City Miami Milan Minneapolis Monterrey Moscow Munich New York Northern Virginia Paris Perth Philadelphia Rome San Francisco São Paulo Shanghai Silicon Valley Singapore Sydney Tokyo Warsaw Washington, D.C. Associated Offices: Budapest Jakarta Riyadh Shanghai FTZ Ulaanbaatar Zagreb. Business Service Centers: Johannesburg Louisville. Legal Services Center: Berlin. For more information see www.hoganlovells.com

Griffin Capital Essential Asset REIT, Inc. - 2 - November 25, 2020

original documents of all documents submitted to us as copies (including pdfs). We also have assumed that the Shares will not be issued in violation of the ownership limit contained in the Company’s First Articles of Amendment and Restatement, as amended. As to all matters of fact, we have relied on the representations and statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing.

This opinion letter is based as to matters of law solely on the Maryland General Corporation Law, as amended. We express no opinion herein as to any other statutes, rules or regulations.

Based upon, subject to and limited by the foregoing, we are of the opinion that following (i) effectiveness of the Registration Statement and (ii) issuance of the Shares by the Company in accordance with the terms of the Merger Agreement, the Shares will be validly issued, fully paid, and nonassessable.

This opinion letter has been prepared for use in connection with the Registration Statement. We assume no obligation to advise of any changes in the foregoing subsequent to the effective date of the Registration Statement.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to the reference to this firm under the caption “Legal Matters” in the prospectus constituting a part of the Registration Statement. In giving this consent, we do not thereby admit that we are an “expert” within the meaning of the Act.

Very truly yours,

/s/ Hogan Lovells US LLP

HOGAN LOVELLS US LLP