Exhibit 5.1

OPINION OF WILSON SONSINI GOODRICH & ROSATI

PROFESSIONAL CORPORATION

January 21, 2021

FireEye, Inc.

601 McCarthy Blvd.

Milpitas, CA 95035

Re: Registration Statement on Form S-8

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-8 (the “Registration Statement”) to be filed by FireEye, Inc., a Delaware corporation (the “Company”), with the Securities and Exchange Commission on or about the date hereof, in connection with the registration under the Securities Act of 1933, as amended, of 841,584 shares of the Company’s common stock (the “Shares”) reserved for issuance pursuant to awards outstanding under the Respond Software, Inc. 2016 Stock Option and Grant Plan, as amended (the “Plan”). As your legal counsel, we have examined the proceedings taken and are familiar with the actions proposed to be taken by you in connection with the issuance and sale of the Shares under the Plan and pursuant to the agreements related thereto.

It is our opinion that, when issued and sold in the manner referred to in the Plan and pursuant to the agreements that accompany the Plan, the Shares will be legally and validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to the use of our name wherever appearing in the Registration Statement and any amendments thereto.

Very truly yours,

WILSON SONSINI GOODRICH & ROSATI

Professional Corporation

/s/ Wilson Sonsini Goodrich & Rosati