Exhibit 5.1

C. Thomas Hopkins

+1 310 883 6417

thopkins@cooley.com

September 6, 2016

Everbridge, Inc.

25 Corporate Drive, Suite 400

Burlington, MA 01803

Ladies and Gentlemen:

We are counsel to Everbridge, Inc., a Delaware corporation (the “Company”), in connection with the filing by the Company of a Registration Statement (No. 333-213217) on Form S-1 (the “Registration Statement”) with the Securities and Exchange Commission, including a related prospectus filed with the Registration Statement (the “Prospectus”), covering an underwritten public offering of (i) up to 6,250,000 shares of the Company’s common stock, par value $0.001 per share (the “Common Stock”), sold by the Company (the “Company Shares”), and (ii) up to 2,375,000 shares of Common Stock sold by certain selling stockholders (the “Stockholder Shares”), including up to up to 1,125,000 shares of Common Stock sold pursuant to the exercise of an of an over-allotment option granted to the underwriters.

In connection with this opinion, we have examined and relied upon (a) the Registration Statement and related Prospectus, (b) the Company’s Amended and Restated Certificate of Incorporation, as amended, and Bylaws, as currently in effect, (c) the Company’s Amended and Restated Certificate of Incorporation, filed as Exhibit 3.2 to the Registration Statement and the Company’s Amended and Restated Bylaws, filed as Exhibit 3.4 to the Registration Statement, each of which will be in effect upon the closing of the offering contemplated by the Registration Statement, and (d) the originals or copies certified to our satisfaction of such records, documents, certificates, memoranda and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness and authenticity of all documents submitted to us as originals and the conformity to originals of all documents submitted to us as copies. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not sought independently to verify such matters. Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware. We express no opinion as to whether the laws of any particular jurisdiction are applicable to the subject matter hereof. We are not rendering any opinion as to compliance with any federal or state antifraud law, rule or regulation relating to securities, or to the sale or issuance thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Company Shares, when sold and issued against payment therefor as described in the Registration Statement and the related Prospectus, will be validly issued, fully paid and non-assessable, and that the Stockholder Shares have been validly issued and are fully paid and non-assessable.

We consent to the filing of this opinion as an exhibit to the Registration Statement.

1333 2ND STREET, SUITE 400, SANTA MONICA, CA 90401  T: (310) 883-6400  F: (310) 883-6500  WWW.COOLEY.COM

Everbridge, Inc.

September 6, 2016

Page Two

We consent to the reference to our firm under the caption “Legal Matters” in the Prospectus included in the Registration Statement and to the filing of this opinion as an exhibit to the Registration Statement.

Sincerely,

1333 2ND STREET, SUITE 400, SANTA MONICA, CA 90401  T: (310) 883-6400  F: (310) 883-6500  WWW.COOLEY.COM