<PAGE>

                                                                   EXHIBIT 31(a)

                    CERTIFICATION OF CHIEF EXECUTIVE OFFICER

     I, Gary M. Mulloy, Chairman and Chief Executive Officer of ADVO, Inc.,
certify that:

     1)  I have reviewed this annual report on Form 10-K of ADVO, Inc. (the
         "registrant");

     2)  Based on my knowledge, this annual report does not contain any untrue
         statement of a material fact or omit to state a material fact necessary
         to make the statements made, in light of the circumstances under which
         such statements were made, not misleading with respect to the period
         covered by this annual report;

     3)  Based on my knowledge, the financial statements, and other financial
         information included in this annual report, fairly present in all
         material respects the financial condition, results of operations and
         cash flows of the registrant as of, and for, the periods presented in
         this annual report;

     4)  The registrant's other certifying officer and I are responsible for
         establishing and maintaining disclosure controls and procedures (as
         defined in Exchange Act Rules 13a-14 and 15d-14) for the registrant and
         we have:

        a)  designed such disclosure controls and procedures, or caused such
            disclosure controls and procedures to be designed under our
            supervision, to ensure that material information relating to the
            registrant, including its consolidated subsidiaries, is made known
            to us by others within those entities, particularly during the
            period in which this annual report is being prepared; and

        b)  evaluated the effectiveness of this registrant's disclosure controls
            and procedures and presented in this annual report our conclusions
            about the effectiveness of the disclosure controls and procedures,
            as of the end of the period covered by this report based on such
            evaluation; and

        c)  disclosed in this annual report any change in the registrant's
            internal control over financial reporting that occurred during the
            registrant's most recent fiscal quarter that has materially
            affected, or is reasonably likely to materially affect, the
            registrant's internal control over financial reporting;

     5)  The registrant's other certifying officer and I have disclosed, based
         on our most recent evaluation of internal control over financial
         reporting, to the registrant's auditors and the audit committee of
         registrant's board of directors (or persons performing the equivalent
         functions):

        a)  all significant deficiencies and material weaknesses in the design
            or operation of internal controls over financial reporting which are
            reasonably likely to adversely affect the registrant's ability to
            record, process, summarize and report financial information; and

        b)  any fraud, whether or not material, that involves management or
            other employees who have a significant role in the registrant's
            internal controls over financial reporting.

                                          /s/ GARY M. MULLOY
                                          --------------------------------------
                                          Gary M. Mulloy
                                          Chairman and Chief Executive Officer

Date: December 19, 2003