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                                                                    EXHIBIT 10.3
                                                                    ------------

                         MACK-CALI REALTY CORPORATION
                          AGREEMENT TO VOTE AND PROXY


     THIS AGREEMENT TO VOTE AND PROXY (this "Agreement") dated as of June 27,
2000, is by and between Michael V. Prentiss, Santo Bisignano, as trustee of PEP
Grantor Retained Annuity Trust, as trustee of MBP Grantor Retained Annuity Trust
and as trustee of KAP Grantor Retained Annuity Trust (collectively
"Shareholder"), and Mack-Cali Realty Corporation ("Mack-Cali").

                                   RECITALS

     A.   Mack-Cali, Mack-Cali Realty, L.P., a Delaware limited partnership
("Mack-Cali Partnership"), Prentiss Properties Trust, a Maryland real estate
investment trust ("Prentiss") and Prentiss Properties Acquisition Partners,
L.P., a Delaware limited partnership ("Prentiss Partnership"), are entering into
an Agreement and Plan of Merger of even date herewith (the "Merger Agreement"),
pursuant to which (i) Prentiss Partnership shall be merged with and into Mack-
Cali Partnership and (ii) Prentiss shall be merged with and into Mack-Cali (the
"Merger").

     B.   As of the date hereof, Shareholder owns, beneficially and of record,
of the outstanding common stock, par value $.01 per share, of Prentiss (the
"Common Stock") set forth on Exhibit A hereto (such shares of Common Stock and
any additional shares of Common Stock owned in the future by Shareholder being
herein referred to as the "Shares").

     C.   In consideration of Mack-Cali's agreement to enter into the Merger
Agreement, Shareholder (i) agrees to vote the Shares in favor of the Merger
(subject to the irrevocable proxy provided for in Section 2 hereof (the
                                                  ---------
"Proxy")), and (ii) grants to Mack-Cali the Proxy covering the Shares to vote in
favor of the Merger, all in accordance with the terms set forth in this
Agreement.

                                   AGREEMENT

     NOW, THEREFORE, in consideration of the foregoing and the representations,
warranties, covenants and agreements contained in this Agreement, the parties
hereto agree as follows:

     1.   Voting Agreement.
          ----------------

          1.1  Agreement to Support Merger. Shareholder agrees to vote the
               ---------------------------
Shares in favor of the Merger, pursuant to the terms of the Merger Agreement, at
the Prentiss Shareholders Meeting (as defined in the Merger Agreement).

          1.2  Applicability of Voting Agreement. The voting agreement contained
               ---------------------------------
in Section 1.1 shall apply to the Shares whether or not owned by Shareholder .
   -----------
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     2.  Proxy with Respect to Shares.  Shareholder hereby irrevocably appoints
         ----------------------------
Mack-Cali as its attorney and proxy, with full power of substitution, to vote in
such manner as such attorney and proxy or its substitute shall, in its sole
discretion, deem proper, and otherwise act with respect to all of the Shares
which it is entitled to vote at any meeting of shareholders (whether annual or
special and whether or not an adjourned meeting) of Prentiss; provided, however,
                                                              --------  -------
that Shareholder grants a proxy hereunder only with respect to the following
matters that may be presented to the shareholders of Prentiss (the "Designated
Matters"): (i) votes with respect to the Merger and the Merger Agreement; (ii)
votes with respect to any action or agreement that would result in a breach of
any covenant, representation or warranty or any other obligation or agreement of
Prentiss under the Merger Agreement; (iii)  votes with respect to any action or
agreement that would impede, interfere with, delay, postpone or attempt to
discourage the Merger and the Merger Agreement, including, but not limited to,
(a) any reorganization or liquidation involving Prentiss, (b) any change in the
board of trustees of Prentiss, except as otherwise agreed to in writing by Mack-
Cali, or (c) any material change in the present capitalization of Prentiss; (iv)
votes relating to any other material change in the corporate structure or
business of Prentiss; and (v) votes in favor and approval of the matter
Shareholder has agreed to vote in favor of in Section 1.1 hereof.  This proxy is
                                              -----------
irrevocable, is coupled with an interest sufficient in law to support an
irrevocable proxy and is granted in consideration of and as an inducement to
cause Prentiss to enter into the transactions contemplated by the Merger
Agreement.  This proxy shall revoke any other proxy granted by Shareholder at
any time with respect to the Shares and no subsequent proxies will be given by
Shareholder with respect to the Shares while the Proxy is in effect.  In
addition, if subsequent to the date hereof Shareholder is entitled to vote the
Shares for any purpose, it shall take all actions necessary to vote the Shares
pursuant to instructions received from Mack-Cali; provided, however, that the
                                                  --------  -------
provisions of this sentence shall only apply to the Designated Matters.  This
proxy shall apply to the Shares whether or not owned by Shareholder.

     3.   Legends. The stock certificates representing the Shares shall bear the
          -------
following legend until the voting agreement contained in Section 1.1 terminates:
                                                         -----------

     "The shares represented by this Certificate are subject to a
     voting agreement and proxy pursuant to an Agreement to Vote and
     Proxy, dated June 27, 2000, between Michael V. Prentiss and Mack-
     Cali Realty Corporation, and any amendments thereof. A copy of
     such agreement is on file at the principal place of business of
     Prentiss Properties Trust ("Prentiss") and a copy will be
     provided to the holder hereof at no cost upon written request to
     the corporate secretary of Prentiss."

     4.   Representations and Warranties of Shareholder.  Shareholder represents
          ---------------------------------------------
and warrants to Mack-Cali as follows:

          4.1  Ownership of Shares. On the date hereof, the Shares are all of
               -------------------
the shares of Prentiss' Common Stock currently beneficially owned by
Shareholder. Shareholder does not have any rights to acquire any additional
shares of Prentiss' Common Stock other than pursuant to existing stock options
granted under Prentiss stock option plans. Until the termination of this
Agreement, Shareholder shall not sell or otherwise transfer any of the Shares;
provided, however,

                                       2
<PAGE>

Shareholder may sell any or all of his Shares and/or options to acquire Shares
immediately prior to the Merger. Shareholder has good, valid and marketable
title to the Shares, free and clear of all liens, encumbrances, restrictions,
options, warrants, rights to purchase and claims of every kind (other than the
encumbrances created by this Agreement, bona fide loan transactions,
restrictions on transfer under applicable Federal and state securities laws and
restrictions on transfer created by any plans of Prentiss under which such
Shares were issued).

          4.2  Power; Binding Agreement. Shareholder has the full legal right,
               ------------------------
power and authority to enter into and perform all of Shareholder's obligations
under this Agreement. The board of trustees of Prentiss has taken all necessary
action to approve the transactions contemplated by this Agreement pursuant to
Section 3-602 of the Maryland General Corporation Law. The execution and
delivery of this Agreement by Shareholder has been authorized by Shareholder and
will not violate any other agreement to which Shareholder is a party, including,
without limitation, any voting agreement, shareholders agreement, voting trust
or proxy. This Agreement has been duly executed and delivered by Shareholder and
constitutes a legal, valid and binding agreement of Shareholder, enforceable in
accordance with its terms, except as the enforcement thereof may be limited by
bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and
similar laws, now or hereafter in effect affecting creditors' rights and
remedies generally or general principles of equity. Neither the execution nor
delivery of this Agreement nor the consummation by Shareholder of the
transactions contemplated hereby will (i) require any consent or approval of or
filing with any governmental or other regulatory body except for filings on
Schedule 13D under the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), or (ii) constitute a violation of, conflict with or constitute
a default under, any contract, commitment, agreement, understanding, arrangement
or other restriction of any kind to which Shareholder is a party or by which
Shareholder is bound.

     5.  Termination.  This Agreement (other than Section 6) shall terminate on
         -----------                              ---------
the earliest of:

               (a)     the date on which Mack-Cali and Shareholder mutually
consent to terminate this Agreement in writing;

               (b)     upon the consummation of the transactions contemplated by
the Merger Agreement; or

               (c)     prior to the consummation of the transactions
contemplated by the Merger Agreement, upon the termination of the Merger
Agreement pursuant to its terms.

     6.  Expenses.  Each party hereto will pay all of its expenses in connection
         --------
with the transactions contemplated by this Agreement.

     7.  Notice of Additional Shares.  Shareholder agrees, while this Agreement
         ---------------------------
is in effect, to notify Mack-Cali promptly of the number of any shares of
Prentiss' Common Stock acquired by Shareholder after the date hereof.

                                       3
<PAGE>

     8.   Notices.  All notices or other communications required or permitted
          -------
hereunder shall be in writing (except as otherwise provided herein) and shall be
deemed duly given when received by delivery in person, by telecopy or by
certified mail, postage prepaid, or by an overnight courier service, addressed
as follows:

          If to Mack-Cali:

               Mack-Cali Realty Corporation
               11 Commerce Drive
               Cranford, New Jersey  07016
               Attention:  Mitchell E. Hersh
               Telecopy:  (214) 969-4343

               with copies to:

               Pryor, Cashman, Sherman & Flynn L.L.P.
               410 Park Avenue, 10th Floor
               New York, New York  10022
               Attention:  Blake Hornick
               Telecopy:  (212) 326-0806

          If to Shareholder:

               Prentiss Properties Trust
               3890 West Northwest Highway, Suite 400
               Dallas, Texas  75220
               Attention:  General Counsel
               Telecopy:  (214) 654-5818

               with copies to:

               Akin, Gump, Strauss, Hauer & Feld, L.L.P.
               1700 Pacific Avenue, Suite 4100
               Dallas, Texas  75201
               Attention:  Michael E. Dillard, P.C.
               Telecopy:  (214) 969-4343

     9.   Entire Agreement; Amendment.  This Agreement, together with the
          ---------------------------
documents expressly referred to herein, constitutes the entire agreement among
the parties hereto with respect to the subject matter contained herein and
supersedes all prior agreements and understandings among the parties with
respect to such subject matter. This Agreement may not be modified, amended,
altered or supplemented except by an agreement in writing executed by the party
against whom such modification, amendment, alteration or supplement is sought to
be enforced.

                                       4
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     10.  Assigns. This Agreement shall be binding upon, and inure to the
          -------
benefit of the parties hereto and their respective successors and permitted
assigns, but neither this Agreement nor any of the rights, interests or
obligations hereunder shall be assigned by any of the parties hereto without the
prior written consent of the other parties.

     11.  Governing Law.  This Agreement, and all matters relating hereto, shall
          -------------
be governed by, and construed in accordance with the laws of the State of
Maryland without giving effect to the principles of conflicts of laws thereof.

     12.  Injunctive Relief.  The parties agree that in the event of a breach of
          -----------------
any provision of this Agreement, the aggrieved party may be without an adequate
remedy at law.  The parties therefore agree that in the event of a breach of any
provision of this Agreement, the aggrieved party may elect to institute and
prosecute proceedings in any court of competent jurisdiction to enforce specific
performance or to enjoin the continuing breach of such provision, as well as to
obtain damages for breach of this Agreement and such aggrieved party may take
any such actions without the necessity of posting a bond.  By seeking or
obtaining such relief, the aggrieved party will not be precluded from seeking or
obtaining any other relief to which it may be entitled.

     13.  Counterparts.  This Agreement may be executed in any number of
          ------------
counterparts, each of which shall be deemed to be an original and all of which
together shall constitute one and the same document.

     14.  Severability.  Any term or provision of this Agreement which is
          ------------
invalid or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such invalidity or unenforceability without
rendering invalid or unenforceable the remaining terms and provisions of this
Agreement or affecting the validity or enforceability of any of the terms or
provisions of this Agreement in any other jurisdiction.  If any provision of
this Agreement is so broad as to be unenforceable such provision shall be
interpreted to be only so broad as is enforceable.

     15.  Further Assurances.  Each party hereto shall execute and deliver such
          ------------------
additional documents as may be necessary or desirable to consummate the
transactions contemplated by this Agreement.

     16.  Third Party Beneficiaries.  Nothing in this Agreement, expressed or
          -------------------------
implied, shall be construed to give any person other than the parties hereto any
legal or equitable right, remedy or claim under or by reason of this Agreement
or any provision contained herein.

           [The remainder of this page is intentionally left blank.]

                                       5
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     IN WITNESS WHEREOF, Mack-Cali and Shareholder have each caused this
Agreement to be executed by their duly authorized officers as of the date and
year first above written.

                                   MACK-CALI REALTY CORPORATION


                                   By: /s/ MITCHELL E. HERSH
                                      ------------------------------------------
                                   Name:   Mitchell E. Hersh
                                        ----------------------------------------
                                   Title:  Chief Executive Officer
                                         ---------------------------------------



                                   SHAREHOLDER



                                   /s/  MICHAEL V. PRENTISS
                                   ---------------------------------------------
                                   Michael V. Prentiss


                                   /s/  SANTO BISIGNANO
                                   ---------------------------------------------
                                   Santo Bisignano
                                   as trustee of PEP Grantor Retained Annuity
                                   Trust



                                   /s/  SANTO BISIGNANO
                                   ---------------------------------------------
                                   Santo Bisignano
                                   as trustee of MBP Grantor Retained Annuity
                                   Trust



                                   /s/  SANTO BISIGNANO
                                   ---------------------------------------------
                                   Santo Bisignano
                                   as trustee of KAP Grantor Retained Annuity
                                   Trust

                                       6
<PAGE>

                                   EXHIBIT A



                              Michael V. Prentiss
                             Beneficial Ownership


          Ownership in Prentiss Properties Trust                 Amount
          --------------------------------------                 ------

          Shares of Common Stock                               1,193,732
          PEP Grantor Retained Annuity Trust                     298,958
          MBP Grantor Retained Annuity Trust                     298,960
          KAP Grantor Retained Annuity Trust                     298,960
                                                            ------------

             Total                                             2,090,610
                                                            ============