


                                                                     Exhibit 5.1

                                                          July 18, 1995

Omnicom Group Inc.
437 Madison Avenue
New York, NY 10022

                     Re: Registration Statement on Form S-4
                         ----------------------------------

Gentlemen:

     In our capacity as counsel to Omnicom  Group Inc.,  a New York  corporation
(the  "Company"),  we have been asked to render this opinion in connection  with
Registration  Statement No. 33-60167 on Form S-4 (the "Registration  Statement")
filed by the Company  with the  Securities  and  Exchange  Commission  under the
Securities  Act of 1933,  as  amended,  covering an  aggregate  of up to 600,000
shares of common  stock,  $0.50 par value,  of the Company (the  "Shares") to be
issued in connection with the acquisition by the Company, through its indirectly
wholly-owned subsidiary TBWA International Inc., of the assets and businesses of
Chiat/Day Holdings, Inc. and Chiat/Day inc. Advertising.

     In that connection,  we have examined the Certificate of Incorporation  and
the  By-Laws,  both as amended,  of the  Company,  the  Registration  Statement,
corporate  proceedings  relating to the  issuance of the Shares,  and such other
instruments and documents as we deemed relevant under the circumstances.

     In making the aforesaid examination, we have assumed the genuineness of all
signatures and the conformity to original  documents of all copies  furnished to
us as original or  photostatic  copies.  We have also assumed that the corporate
records  furnished to us by the Company include all corporate  proceedings taken
by the Company to date.

     Based upon and subject to the  foregoing,  we are of the opinion  that when
issued in accordance with the Acquisition  Agreement,  the Shares will have been
legally  issued and be fully  paid and  non-assessable  shares of common  stock,
$0.50 par value, of the Company.

     We hereby  consent  to the use of our  opinion  as  herein  set forth as an
exhibit  to the  Registration  Statement  and to the use of our name  under  the
caption "Legal Matters" in the Prospectus/Information  Statement forming part of
the Registration Statement.

                                                        Very truly yours,

                                                        DAVIS & GILBERT

