<PAGE>

                                                                   Exhibit 10.14


                    SEVENTH AMENDMENT TO AMENDED AND RESTATED
                        AGREEMENT OF LIMITED PARTNERSHIP
                                       OF
                     BRANDYWINE OPERATING PARTNERSHIP, L.P.


                  THIS SEVENTH AMENDMENT, dated as of December 31, 1998 (the
"Amendment"), amends the Amended and Restated Agreement of Limited Partnership
(as heretofore amended to date, the "Partnership Agreement") of BRANDYWINE
OPERATING PARTNERSHIP, L.P., a Delaware limited partnership (the "Partnership").
Capitalized terms used herein but not defined herein shall have the meanings
given such terms in the Partnership Agreement.

                                   BACKGROUND

         A. Pursuant to the Partnership Agreement, Brandywine Realty Trust (the
"General Partner"), as the general partner of the Partnership, has the power and
authority to issue additional Partnership Interests to persons on such terms and
conditions as the General Partner may deem appropriate.

         B. The General Partner, pursuant to the exercise of such power and
authority and in accordance with the Partnership Agreement, has determined to
execute this Amendment to the Partnership Agreement to evidence the issuance of
additional Partnership Interests and the admission of the other signatories
hereto as Limited Partners of the Partnership in exchange for certain
contributions of partnership interests in partnerships holding real estate and
real estate related assets that are being made to the Partnership on the date
hereof pursuant to a "contribution" agreement (relating to a property commonly
known as Interstate Center) among the Partnership, the General Partner and the
Admitted Partners (as defined below).

                  NOW, THEREFORE, in consideration of the mutual covenants and
agreements herein contained and other good and valuable consideration, the
receipt, adequacy and sufficiency of which are hereby acknowledged, the parties
hereto, intending to be legally bound, hereby amend the Partnership Agreement as
follows:

                  1. The Partnership Agreement is hereby amended to reflect the
admission as a Limited Partner on the date hereof of the Persons set forth on
Schedule A attached hereto (the "Admitted Partners") and the ownership by such
Persons of the number of Class A Units listed opposite each Person's name on
Schedule A. Attached as Schedule B is a list of the Partners of the Partnership
prior to the admission of the Admitted Partners, together with the number and
class of Partnership Interests owned by such partners.


<PAGE>

                  2. The Partnership Interests issued hereby shall constitute
Class A Units; provided that any distribution to be received by the Admitted
Partners on the Class A Units issued to them on the date hereof on account of
the fiscal quarter in which they are admitted to the Partnership shall be
pro-rated to reflect the portion of the fiscal quarter of the Partnership for
which the Admitted Partners held such Class A Units and shall not be pro-rata in
accordance with their then Percentage Interests; provided further that the
Redemption Right granted to holders of Class A Units in Article XV of the
Partnership Agreement shall not be exercisable by the holders of the Class A
Units issued on the date hereof to the Admitted Partners until 180 days after
the date hereof, except that, (i) if the holder of any such Class A Units dies,
such holder's estate shall thereupon be permitted to exercise the Redemption
Right with respect to all of such Class A Units held by it notwithstanding the
foregoing restriction and (ii) if a Change of Control (as defined below) of the
General Partner occurs, the foregoing restriction on exercise of the Redemption
Right shall automatically terminate with respect to all of such Class A Units.

                  3. As used herein, the term "Change of Control" shall mean
Change of Control" means:

                     (i)   the acquisition in one or more transactions by any
                           "Person" (as the term person is used for purposes of
                           Sections 13(d) or 14(d) of the Exchange Act) of
                           "Beneficial ownership" (within the meaning of Rule
                           13d-3 promulgated under the Exchange Act) of
                           twenty-five percent (25%) or more of the combined
                           voting power of the General Partner's then
                           outstanding voting securities (the "Voting
                           Securities"), provided that for purposes of this
                           clause (i) Voting Securities acquired directly from
                           the General Partner by any Person shall be excluded
                           from the determination of such Person's Beneficial
                           ownership of Voting Securities (but such Voting
                           Securities shall be included in the calculation of
                           the total number of Voting Securities then
                           outstanding); or

                     (ii)  approval by shareholders of the General Partner of:

                           (A)  a merger, reorganization or consolidation
                                involving the General Partner if the
                                shareholders of the General Partner immediately
                                before such merger, reorganization or
                                consolidation do not or will not own directly or
                                indirectly immediately following such merger,
                                reorganization or consolidation, more than fifty
                                percent (50%) of the combined voting power of
                                the outstanding voting securities of the General
                                Partner resulting from or surviving such merger,
                                reorganization or consolidation in substantially
                                the same proportion as their ownership of the
                                Voting Securities outstanding immediately before
                                such merger, reorganization or consolidation; or

                           (B)  a complete liquidation or dissolution of the
                                General Partner; or

                           (C)  an agreement for the sale or other disposition
                                of all or substantially all of the assets of the
                                General Partner; or

                                      -2-
<PAGE>

                     (iii) acceptance by shareholders of the General Partner of
                           shares in a share exchange if the shareholders of the
                           General Partner immediately before such share
                           exchange do not or will not own directly or
                           indirectly immediately following such share exchange
                           more than fifty percent (50%) of the combined voting
                           power of the outstanding voting securities of the
                           entity resulting from or surviving such share
                           exchange in substantially the same proportion as
                           their ownership of the Voting Securities outstanding
                           immediately before such share exchange.

                  4. By execution of this Amendment to the Partnership Agreement
by the General Partner and the Admitted Partners, the Admitted Partners agree to
be bound by each and every term of the Partnership Agreement as amended from
time to time in accordance with the terms of the Partnership Agreement.

                  5. On the date of this Amendment, each of the Admitted
Partners shall execute and deliver to Brandywine Realty Trust an Irrevocable
Proxy coupled with an Interest in the form set forth on Exhibit 1 hereto
attached.

                  6. This Amendment may be executed in one or more counterparts,
each such counterpart being deemed to be an original instrument, and all such
counterparts together constituting the same agreement.

                  7. Except as expressly set forth in this Amendment to the
Partnership Agreement, the Partnership Agreement is hereby ratified and
confirmed in each and every respect.

                  IN WITNESS WHEREOF, this Amendment to the Partnership
Agreement has been executed and delivered as of the date first above written.

                                  GENERAL PARTNER:

                                  BRANDYWINE REALTY TRUST


                                  By:
                                       ------------------------------------
                                       Gerard H. Sweeney, President and CEO


                                  ADMITTED PARTNERS:


                                  -----------------------------------------
                                  William H. Godwin, Jr.


                                  -----------------------------------------
                                  Bryson Powell



                                      -3-
<PAGE>


                                  SCHEDULE "A"

                                                   NUMBER OF
                    ADMITTED                      PARTNERSHIP
                    PARTNERS                       INTERESTS
                    --------                       ---------

             William H. Godwin, Jr.                  41,734

                  Bryson Powell                      41,734


























                                      -4-
<PAGE>

                                  SCHEDULE "B "

                     BRANDYWINE OPERATING PARTNERSHIP, L.P.
                        OUTSTANDING PARTNERSHIP INTERESTS
                             AS OF DECEMBER 31, 1998
<TABLE>
<CAPTION>

                                                                NUMBER OF PARTNERSHIP
                                                                INTERESTS (ALL CLASS A UNITS
LIMITED PARTNERS                                                UNLESS OTHERWISE INDICATED)
----------------                                                ---------------------------
<S>                                                                    <C>
The Nichols Company                                                    2,742
Brian F. Belcher                                                       7,245
Jack R. Loew                                                           1,245
Craig C. Hough                                                         1,245
Werner A. Fricker                                                      6,830
Randle Scarborough                                                     59,578
Sean Scarborough                                                       60,576
Steven L. Shapiro                                                      1,902
Robert K. Scarborough                                                  215,384
Raymond J. Perkins                                                     2,536
Brandywine Holdings I, Inc.                                            5
Brandywine Realty Trust                                                467,220
Brookstone Investors, L.L.C.                                           57,126
Brookstone Holdings of Del.-4, L.L.C.                                  7,579
Brookstone Holdings of Del.-5, L.L.C.                                  80,445
Brookstone Holdings of Del.-6, L.L.C.                                  7,886
John S. Trogner, Sr.                                                   89,801.232
John S. Trogner, Jr.                                                   73,048.310
Blair S. Trogner, Sr.                                                  138,126.471
Emma B. Trogner                                                        27,087.416
Ronalee Trogner                                                        21,669.933
Candis C. Trogner                                                      40,631.123
Donald E. Axinn                                                        928,651
Morris Green                                                           50,233
Arthur and Marion Eberstein, Joint Tenants                             7,513
Lennard Axinn                                                          2,156
Trust UTW of Theodore Geffner                                          485
Howard Kantor                                                          31,505
Irving Hirschman Family Trust                                          1,488
Leo Guthart                                                            876
Gloria Kantor                                                          21,647
Richard Bernhard                                                       40,927
Calvin Axinn                                                           40,927
Helen Geffner                                                          1,488
Brandywine Realty Trust                                                750,000  Series A Preferred
                                                                                Mirror Units
Commonwealth Atlantic Operating Properties Inc.                        1,140,527  Series B Preferred
                                                                                  Units
Commonwealth Atlantic Land II Inc.                                     283,731  Series B Preferred
                                                                                Units
Commonwealth Atlantic Development Inc.                                 43,725  Series B Preferred
                                                                               Units
Commonwealth Atlantic Land Company                                     82,017  Series B Preferred
                                                                               Units

<CAPTION>
GENERAL PARTNER                                                 NUMBER OF PARTNERSHIP INTERESTS
---------------                                                 -------------------------------

<S>                                                                    <C>
Brandywine Realty Trust                                                37,549,713 GP Units
</TABLE>



                                      -5-
<PAGE>

                                    EXHIBIT 1

                   IRREVOCABLE PROXY COUPLED WITH AN INTEREST


                  KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby
irrevocably constitutes and appoints the General Partner, any Liquidating
Trustee, and authorized officers and attorneys-in-fact of each, and each of
those acting singly, in each case with full power of substitution, as its true
and lawful agent and attorney-in-fact, with full power and authority in its
name, place and stead to: execute, swear to, acknowledge, deliver, file and
record in the appropriate public offices (i) all certificates, documents and
other instruments (including, without limitation, this Agreement and the
Certificate and all amendments or restatements thereof) that the General Partner
or the Liquidating Trustee deems appropriate or necessary to form, qualify or
continue the existence or qualification of the Partnership as a limited
partnership (or a partnership in which the limited partners have limited
liability) in the State of Delaware and in all other jurisdictions in which the
Partnership may conduct business or own property; (ii) all instruments that the
General Partner deems appropriate or necessary to reflect any amendment, change,
modification or restatement of this Agreement in accordance with its terms;
(iii) all conveyances and other instruments or documents that the General
Partner deems appropriate or necessary to reflect the dissolution and
liquidation of the Partnership pursuant to the terms of this Agreement,
including, without limitation, a certificate of cancellation; and (iv) all
instruments relating to the admission, withdrawal, removal or substitution of
any Partner pursuant to the provisions of this Agreement, or the Capital
Contribution of any Partner. The foregoing power of attorney is irrevocable and
a power coupled with an interest, in recognition of the fact that each of the
Partners will be relying upon the power of the General Partner to act as
contemplated by this Agreement in any filing or other action by it on behalf of
the Partnership, and it shall survive the death, incapacity or incompetency of a
Limited Partner to the effect and extent permitted by law and the Transfer of
all or any portion of such Limited Partner's Partnership Units and shall extend
to such Limited Partner's heirs, distributees, successors, assigns and personal
representatives.

                  IN WITNESS WHEREOF, the undersigned has executed and delivered
this Proxy on this 31st day of December, 1998.


                                        ---------------------------------
                                        William H. Godwin, Jr.



                                      -6-
<PAGE>


                                    EXHIBIT 1

                   IRREVOCABLE PROXY COUPLED WITH AN INTEREST


                  KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby
irrevocably constitutes and appoints the General Partner, any Liquidating
Trustee, and authorized officers and attorneys-in-fact of each, and each of
those acting singly, in each case with full power of substitution, as its true
and lawful agent and attorney-in-fact, with full power and authority in its
name, place and stead to: execute, swear to, acknowledge, deliver, file and
record in the appropriate public offices (i) all certificates, documents and
other instruments (including, without limitation, this Agreement and the
Certificate and all amendments or restatements thereof) that the General Partner
or the Liquidating Trustee deems appropriate or necessary to form, qualify or
continue the existence or qualification of the Partnership as a limited
partnership (or a partnership in which the limited partners have limited
liability) in the State of Delaware and in all other jurisdictions in which the
Partnership may conduct business or own property; (ii) all instruments that the
General Partner deems appropriate or necessary to reflect any amendment, change,
modification or restatement of this Agreement in accordance with its terms;
(iii) all conveyances and other instruments or documents that the General
Partner deems appropriate or necessary to reflect the dissolution and
liquidation of the Partnership pursuant to the terms of this Agreement,
including, without limitation, a certificate of cancellation; and (iv) all
instruments relating to the admission, withdrawal, removal or substitution of
any Partner pursuant to the provisions of this Agreement, or the Capital
Contribution of any Partner. The foregoing power of attorney is irrevocable and
a power coupled with an interest, in recognition of the fact that each of the
Partners will be relying upon the power of the General Partner to act as
contemplated by this Agreement in any filing or other action by it on behalf of
the Partnership, and it shall survive the death, incapacity or incompetency of a
Limited Partner to the effect and extent permitted by law and the Transfer of
all or any portion of such Limited Partner's Partnership Units and shall extend
to such Limited Partner's heirs, distributees, successors, assigns and personal
representatives.

                  IN WITNESS WHEREOF, the undersigned has executed and delivered
this Proxy on this 31st day of December, 1998.


                                        ---------------------------------
                                        Bryson Powell


                                      -7-