<PAGE>

                                                                    EXHIBIT 10.3

                            PRENTISS PROPERTIES TRUST
                           AGREEMENT TO VOTE AND PROXY

         THIS AGREEMENT TO VOTE AND PROXY (this "AGREEMENT") dated as of June
27, 2000, is by and between William L. Mack, Mitchell E. Hersh, Earle Mack,
Fredric Mack and David Mack (collectively "SHAREHOLDER"), and Prentiss
Properties Trust, a Maryland real estate investment trust ("PRENTISS").

                                    RECITALS

         A. Mack-Cali Realty Corporation, a Maryland real estate investment
trust ("MACK-CALI"), Mack-Cali Realty, L.P., a Delaware limited partnership
("MACK-CALI PARTNERSHIP"), 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 Mack-Cali (the
"COMMON STOCK") and units of beneficial interest of Mack-Cali Partnership
("UNITS") 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" and such Units and any additional Units owned
in the future by Shareholder being herein referred to as "PARTNERSHIP UNITS").

         C. In consideration of Prentiss' 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")), (ii) grants to Prentiss the Proxy covering the Shares to vote in
favor of the Merger, (iii) agrees to vote their Partnership Units in favor of
the limited partnership agreement of Mack-Cali Partnership if necessary to
effect the mergers contemplated by the Merger Agreement and to grant any
necessary consents and (iv) agrees to vote their Partnership Units in favor of
the Mack-Cali Partnership issuing pari passu partnership units contemplated by
the Merger Agreement and to grant any necessary consents, 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:
<PAGE>

         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 Mack-Cali 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.

                  1.3 AGREEMENT RELATED TO MACK-CALI PARTNERSHIP. Shareholder
agrees to vote their Partnership Units in favor of (i) the transactions
contemplated by the Merger Agreement that may be necessary under the limited
partnership agreement of Mack-Cali Partnership and to grant any necessary
consents related thereto and (ii) the Mack-Cali Partnership issuing up to $245
million in face amount of pari passu partnership units contemplated by the
Merger Agreement and to grant any necessary consents related thereto.

         2. PROXY WITH RESPECT TO SHARES. Shareholder hereby irrevocably
appoints Prentiss 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
Mack-Cali; PROVIDED, HOWEVER, that Shareholder grants a proxy hereunder only
with respect to the following matters that may be presented to the
shareholders of Mack-Cali (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 Mack-Cali 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 Mack-Cali, (b) any change in the
board of directors of Mack-Cali, except as otherwise agreed to in writing by
Prentiss, or (c) any material change in the present capitalization of
Mack-Cali; (iv) votes relating to any other material change in the corporate
structure or business of Mack-Cali; 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 Mack-Cali 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 Prentiss; 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 or
Partnership Units shall bear the following legend until the voting agreement
contained in SECTION 1.1 terminates:


                                       2
<PAGE>

         "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 William L. Mack, Mitchell E. Hersh, Earle Mack,
         Fredric Mack and David Mack and Prentiss Properties Trust, and any
         amendments thereof. A copy of such agreement is on file at the
         principal place of business of Mack-Cali Realty Corporation
         ("Mack-Cali") and a copy will be provided to the holder hereof at no
         cost upon written request to the corporate secretary of Mack-Cali."

         4. REPRESENTATIONS AND WARRANTIES OF SHAREHOLDER. Shareholder
represents and warrants to Prentiss as follows:

                  4.1 OWNERSHIP OF SHARES. On the date hereof, the Shares are
all of the shares of Mack-Cali's Common Stock currently beneficially owned by
Shareholder. Shareholder does not have any rights to acquire any additional
shares of Mack-Cali's Common Stock other than pursuant to existing stock options
granted under Mack-Cali stock option plans. Until the termination of this
Agreement, Shareholder shall not sell or otherwise transfer any of the Shares;
provided, however, 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 Mack-Cali
under which such Shares were issued).

                  4.2 OWNERSHIP OF PARTNERSHIP UNITS. On the date hereof, the
Partnership Units are all of the units of Mack-Cali Partnership currently
beneficially owned by Shareholder. Shareholder does not have any rights to
acquire any additional units of Mack-Cali Partnership. Until the termination of
this Agreement, Shareholder shall not sell or otherwise transfer any of the
Partnership Units; provided, however, Shareholder may sell any or all of his
Partnership Units immediately prior to the Merger. Shareholder has good, valid
and marketable title to the Partnership Units, 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 Mack-Cali
under which such Partnership Units were issued).

                  4.3 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 directors of Mack-Cali 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


                                       3
<PAGE>

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 Prentiss 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 Prentiss promptly of the number of any shares
of Mack-Cali's Common Stock acquired by Shareholder after the date hereof.

         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 Prentiss:

                           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


                                       4
<PAGE>

                  If to Shareholder:

                           Mack-Cali Realty Corporation
                           11 Commerce Drive
                           Cranford, New Jersey  07016
                           Telecopy:  (908) 272-6755

                           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

         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.

         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


                                       5
<PAGE>

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.]


                                       6
<PAGE>

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

                             PRENTISS PROPERTIES TRUST


                             By: /s/ Michael V. Prentiss
                                -----------------------------------
                             Name: Michael V. Prentiss
                                  ---------------------------------
                             Title: Chairman
                                   --------------------------------


                             SHAREHOLDERS


                             /s/ William L. Mack
                             ---------------------------------------
                             William L. Mack


                             /s/ Mitchell E. Hersh
                             ---------------------------------------
                             Mitchell E. Hersh


                             /s/ Earle Mack
                             ---------------------------------------
                             Earle Mack


                             /s/ Fredric Mack
                             ---------------------------------------
                             Fredric Mack


                             /s/ David Mack
                             ---------------------------------------
                             David Mack


                                       7
<PAGE>

                                                                       EXHIBIT A

                  OUTSTANDING COMMON STOCK, PARTNERSHIP UNITS,
                        UNIT WARRANTS, STOCK WARRANTS AND
                       STOCK OPTIONS OWNED BY SHAREHOLDER

<TABLE>
<S>                        <C>                                <C>
WILLIAM L. MACK

                           COMMON UNITS:                      1,345,411
                           PREFERRED UNITS (AS CONVERTED):    2,431,140
                           VESTED UNIT WARRANTS:              679,150
                           VESTED COMMON STOCK OPTIONS:       10,000

MITCHELL E. HERSH

                           VESTED RESTRICTED COMMON STOCK:    9,375
                           COMMON UNITS:                      46,215
                           PREFERRED UNITS (AS CONVERTED):    75,209
                           VESTED COMMON STOCK WARRANTS:      203,985

EARLE MACK

                           COMMON UNITS:                      797,884
                           PREFERRED UNITS (AS CONVERTED):    1,463,838
                           VESTED UNIT WARRANTS:              410,195
                           VESTED COMMON STOCK  OPTIONS:      10,000

FREDRIC MACK

                           COMMON UNITS:                      321,167
                           PREFERRED UNITS (AS CONVERTED):    576,941
                           VESTED UNIT WARRANTS:              161,889

DAVID MACK

                           COMMON UNITS:                      842,517
                           PREFERRED UNITS (AS CONVERTED):    1,521,298
                           VESTED UNIT WARRANTS:              425,664
</TABLE>