<PAGE>   1
                                                                   EXHIBIT 10.15

                                     MASTER
                              EMPLOYMENT AGREEMENT



          THIS EMPLOYMENT AGREEMENT (this "Agreement"), is made and entered into
on this 1st day of June, 1998, by and between JOHN A. WILLIAMS, an individual
resident of the State of Georgia ("Executive"), POST PROPERTIES, INC., a Georgia
corporation ("Post"), POST APARTMENT HOMES, L.P., a Georgia limited partnership
("Post LP") and Post Services, Inc., a Georgia corporation ("Services");


                              W I T N E S S E T H:


          WHEREAS, Post, Post LP and Services desire to employ Executive, and
Executive desires to be employed by Post, Post LP and Services on the terms and
conditions contained in this Agreement;

          NOW, THEREFORE, in consideration of the mutual promises and agreements
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Post, Post LP, Services and
Executive, intending to be legally bound, do hereby agree as follows:

                                     ss. 1.

                                   Employment

          Subject to the terms of this Agreement, Post, Post LP and Services
hereby employ Executive, and Executive hereby accepts such employment with Post,
Post LP and Services. Executive shall serve as Chief Executive Officer of Post,
Post LP and Services. Executive shall report to the Board of Directors of Post
with respect to his duties and responsibilities as Post's Chief Executive
Officer, to the Board of Directors of Post LP's General Partner, Post GP
Holdings, Inc., with respect to his duties and responsibilities as Post LP's
Chief Executive Officer and to the Board of Directors of Services with respect
to his duties and responsibilities as Services' Chief Executive Officer. Subject
to the other terms and conditions of this Agreement, Executive, Post, Post LP
and Services agree that Executive's compensation, accountabilities, and
requirements shall be determined by Post's Board of Directors or its
Compensation Committee (the "Committee"), in their sole discretion but after
discussion with Executive, Post LP and Services. Executive shall devote his
primary business time, skills, and best efforts to rendering services on behalf
of Post, Post LP and Services and their affiliates and shall exercise such care
as is customarily required by executives undertaking similar duties for entities
similar to Post, Post LP and Services. Unless agreed to by Executive, neither
Post, Post LP nor Services will change Executive's job title during the term of
this

                                      

<PAGE>   2



Agreement. Finally, Executive shall have the discretion to decide at any time
whether he is performing his duties or exercising his responsibilities for Post,
for Post LP or for Services.

                                     ss. 2.

                             Compensation; Expenses

          2.1. Base Salary. Commencing on the Effective Date (as defined in
ss. 3.1), Executive shall be paid during the term of Executive's employment
under this Agreement, a minimum base salary equal to $325,000 per annum (the
"Base Salary"), which amount shall be subject to upward adjustment, if any, in
accordance with this ss. 2.1. The Committee shall review Executive's Base Salary
on a regular basis to ensure its continued competitiveness based on the annual
Compensation Performance Matrix adopted by Post, Post LP and Services.
Executive's Base Salary, less all applicable withholding taxes, shall be paid to
Executive in accordance with the payroll procedures in effect with respect to
executive officers of Post but shall be apportioned between and actually be paid
on Post's payroll, Post LP's payroll and Services' payroll as agreed upon from
time to time by Post, Post LP and Services.

          2.2. Option in Lieu of Base Salary. Executive before the beginning of
any calendar year may make an irrevocable election to reduce his Base Salary for
such calendar year by up to $75,000 and to receive instead options to purchase
whole shares of Post common stock. Any such election shall be made in writing
and shall be delivered to the Secretary of Post. Such options thereafter shall
be granted by the Committee under Post's stock option plan at the first regular
meeting of such Committee in such calendar year, and the number of whole shares
of stock subject to such options shall be determined by dividing the amount by
which Executive elected to reduce his Base Salary by the fair market value of a
share of common stock on the date of such Committee meeting. Such fair market
value shall be determined by the Committee under the terms of such stock option
plan, and the option price of such option shall be the same as such fair market
value. Each option shall be exercisable in full at grant and shall (subject to
the plan)remain exercisable until the tenth anniversary of the date of grant and
shall be subject to such other terms and conditions as the Committee deems
appropriate under the circumstances. Cash shall be paid to Executive in lieu of
an option to purchase a fractional share, and such payment shall be made as soon
as practicable after the option is granted under this ss. 2.2.

          2.3. Incentive Compensation. In addition to the Base Salary payable to
Executive pursuant to ss. 2.1, effective as of the Effective Date, Executive
shall be entitled to participate in the following incentive compensation plans:

          (a) Annual Incentive Plan. Executive shall have the opportunity to
     participate in the annual incentive plan, if any, maintained by Post, Post
     LP and Services, the earnings opportunities and performance requirements
     for which will be set out in the annual Compensation Performance Matrix
     adopted by each such company. At the sole discretion of Post's Board of
     Directors, any such annual incentive payments may be paid to Executive

                                       -2-

<PAGE>   3



     in cash, Post stock, or any combination thereof. At the election of
     Executive, any such annual incentive payments, in whole or in part, may be
     deferred according to the deferred compensation plan, if any, maintained by
     Post.

          (b) Long Term Incentive Plan. Executive shall have the opportunity to
     participate in the long term incentive plan, if any, maintained by Post,
     Post LP and Services the earnings opportunities and performance
     requirements for which will be set out in the annual Compensation
     Performance Matrix adopted by each such company.

          2.4. Stock Options. Any options granted on any date to Executive to
purchase Post stock shall be subject to the same terms and conditions as the
stock options granted on the same date to similarly situated executives of Post,
Post LP or Services.

          2.5. Expenses. Executive shall be reimbursed for all reasonable
business-related expenses incurred by Executive at the request of or on behalf
of Post, Post LP or Services, including, without limitation, first class travel
expenses incurred in connection with the performance of Executive's duties and
responsibilities, moving expenses and his expenses to maintain a complete, real
time communications link with Post, Post LP and Services while he is away from
his office.

          2.6. Participation in Employee Benefit Plans.

          (a) General. Executive shall be entitled to participate in such
     medical, dental, disability, hospitalization, life insurance, profit
     sharing and other employee benefit plans as maintained from time to time
     for the benefit of executive officers of Post, Post LP and Services, on the
     terms and subject to the conditions set forth in such plans. However, if
     Post, Post LP and Services each maintain the same plan, the benefits
     available under such plan shall not exceed the benefit which would have
     been available if Post, Post LP and Services were one and the same company.

          (b) Life Insurance. Post, Post LP and Services collectively will
     provide Executive with a split dollar life insurance program up to
     $20,000,000 on terms and conditions to be agreed upon by Post and
     Executive.

          (c) Disability. Post, Post LP and Services collectively will provide
     Executive with a supplemental disability program providing a maximum
     monthly payment of $25,000.

          (d) Annual Physical. Post, Post LP and Services will reimburse
     Executive for a comprehensive physical examination on an annual basis.
     Post, Post LP and Services require that Executive have such an examination
     at least every other year.

          2.7. Vacation. Executive shall receive such paid time off each year
during the term of this Agreement as the Committee deems consistent with his
status as a Chief Executive Officer.

                                       -3-

<PAGE>   4




          2.8. Miscellaneous Perquisites.

          (a) Luncheon/Athletic Club. Post, Post LP and Services collectively
     shall reimburse Executive for monthly dues for one luncheon or athletic
     club.

          (b) Luxury Car. Post, Post LP and Services collectively shall
     reimburse Executive for the rental and operation of a luxury automobile,
     including lease payments, insurance, maintenance, and operating expenses.

          (c) Office. Post, Post LP and Services collectively shall provide a
     senior executive business office and all related equipment and services,
     including secretarial and other support services, to operate and maintain
     such an office during Post's normal work day which is at least comparable
     to the office, equipment and services provided similarly situated senior
     executives of Post and, further, shall provide and maintain home office
     equipment to and for Executive, including a computer, telephone, home
     security system, and related ancillary equipment such as a printer, modem,
     fax machine, and pager to enable Executive to perform his duties and
     responsibilities from his primary residence and each other residence owned
     and used as a secondary residence by Executive.

          (d) Personal Financial Counseling. Post, Post LP and Services
     collectively shall reimburse Executive for all reasonable costs associated
     with retaining a personal financial counselor, up to an annual amount of
     $75,000, to provide such advice and services to and on behalf of Executive
     as customarily provided by personal financial counselors.

          2.9. Allocation. Post, Post LP and Services shall allocate the
payments and benefits called for under this Agreement between themselves as
Post, Post LP and Services deem reasonable and appropriate and, further, may (as
between themselves) designate one company to make all such payments (except with
respect to Base Salary under ss. 2.1 and incentive compensation under ss. 2.3)
and provide all such benefits to Executive. However, Executive may (except with
respect to Base Salary under ss. 2.1 and incentive compensation under ss. 2.3)
look to either Post, Post LP or Services for 100% of the payments and benefits
called for under this Agreement if at any time there is any failure by Post,
Post LP or Services to make any payment or provide any benefit called for under
this Agreement.

                                     ss. 3.

                               Term of Employment

          3.1. Term of Employment. Unless earlier terminated in accordance with
ss. 3.4 or ss. 5 of this Agreement, the employment of Executive under this
Agreement shall commence on June 1, 1998 (the "Effective Date"), and shall
continue for a period of three (3) years through May 31, 2001 (the "Initial
Term").

                                       -4-

<PAGE>   5




          3.2. Renewal. Unless terminated earlier in accordance with ss. 3.4 or
ss. 5, this Agreement on May 31, 2001 and on each anniversary of such date shall
automatically renew for a one (1) additional year term unless either Post or
Executive notifies the other in writing at least six (6) months prior to May 31,
2001 or any anniversary of such date of its or his desire not to renew this
Agreement.

          3.3. Termination of Prior Employment Agreement. Executive's Employment
Agreements with Post, Post LP and Services entered into on July 22, 1993, will
terminate on the Effective Date, but Executive's Noncompetition Agreement with
Post, Post LP and Services, entered into as of July 22, 1993 (the
"Noncompetition Agreement"), shall not be affected by this Agreement and shall
continue in full force and effect.

          3.4. Termination. Except as provided in ss. 5 of this Agreement,
Executive's employment under this Agreement may be terminated as follows:

          (a) by Post upon the death or total disability of Executive (total
     disability meaning the inability of Executive to perform the essential
     functions of his jobs (even with reasonable accommodation) under this
     Agreement for a period of six (6) consecutive months during the term of
     this Agreement by reason of Executive's mental or physical disability)
     (which shall be referred to as a "Death or Disability Termination"); or

          (b) by Post if (i) Executive is convicted of, pleads guilty to, or
     confesses to any felony or any act of fraud, misappropriation or
     embezzlement which has an immediate and materially adverse effect on Post,
     Post LP or Services or any of their affiliates, as determined by Post's
     Board of Directors in good faith; (ii) Executive engages in a fraudulent
     act to the material damage or prejudice of Post, Post LP or Services or any
     of their affiliates or in conduct or activities materially damaging to the
     property, business or reputation of Post, Post LP or Services or any of
     their affiliates, all as determined by Post's Board of Directors in good
     faith; (iii) there is any material act or omission by Executive involving
     malfeasance or negligence in the performance of Executive's duties to Post,
     Post LP or Services to the material detriment of Post, Post LP or Services,
     as determined by Post's Board of Directors in good faith, which has not
     been corrected by Executive within thirty (30) days after written notice
     from Post of any such act or omission; (iv) Executive fails to comply in
     any material respect with the terms of this Agreement or any other
     agreement with Post, Post LP or Services or any of their affiliates or any
     written policies or directives of Post's Board of Directors as determined
     by Post's Board of Directors in good faith, which has not been corrected by
     Executive within thirty (30) days after written notice from Post of such
     failure; or (v) Executive breaches any of the covenants set forth in the
     Noncompetition Agreement (which shall be referred to individually and
     collectively as a "For Cause Termination"); or

          (c) by Post for any reason other than a For Cause Termination or a
     Death or Disability Termination (which shall be referred to as a "No Cause
     Termination"); or

                                       -5-

<PAGE>   6




          (d) by Executive for any reason other than an Executive-Initiated
     Termination (as defined in ss. 3.4(e)) at any time during or after the
     Initial Term and after giving 30 days prior written notice to Post (which
     shall be referred to as a "Voluntary Termination"); or

          (e) by Executive if (i) there is a material reduction in Executive's
     duties, rights, or responsibilities under this Agreement without his
     consent and without regard to whether he keeps his title as Chief Executive
     Officer; (ii) there is a material decrease in the value of Executive's
     compensation and benefits package without his consent; or (iii) Post, Post
     LP or Services accelerates the date for repayment of any indebtedness owed
     by Executive to Post, Post LP or Services without Executive's consent
     (which shall be referred to individually and collectively as an
     "Executive-Initiated Termination").

                                     ss. 4.

                              Result of Termination

          4.1. Termination As Result of Voluntary Termination or For Cause
Termination. If Executive's employment under this Agreement is terminated as a
result of a Voluntary Termination or a For Cause Termination, Executive shall
not thereafter be entitled to receive any Base Salary or other incentive
compensation for periods following the effective date of such termination;
provided, however, that Executive shall be entitled to receive any Base Salary
which may be owed to Executive but is unpaid as of the effective date of such
termination. All Executive's perquisites and benefits called for exclusively
under the terms of this Agreement shall terminate as of the effective date of
such termination. All Executive's perquisites and benefits, including stock
options, to which Executive has a right independent of this Agreement shall
remain in effect, if at all, exclusively under the terms and conditions of the
plans and programs under which such perquisites and benefits were granted to
Executive.

          4.2. Termination As Result of No Cause Termination or
Executive-Initiated Termination. If Executive's employment under this Agreement
is terminated in any calendar year as a result of a No Cause Termination or an
Executive-Initiated Termination,

          (a) Executive shall be entitled to receive (i) any Base Salary which
     is payable for periods ending on or before the effective date of
     Executive's termination but which has not been paid by the effective date
     of such termination, (ii) any stock options to be granted in such calendar
     year in lieu of salary or bonus, (iii) an annual incentive payment of a pro
     rata portion of Executive's annual incentive payment, if any, for the
     preceding calendar year through the effective date of such termination (a
     "Pro Rata Bonus"), and (iv) a severance payment equal to two times
     Executive's Total Annual Compensation for such calendar year. Executive's
     "Total Annual Compensation" for any calendar year shall be equal to his
     Base Salary and annual incentive payment, if any, for the preceding
     calendar year plus the amount of any

                                       -6-

<PAGE>   7



     Base Salary or bonus for such year which he elected to forego in exchange
     for the grant of stock options;

          (b) Executive's unvested stock options, if any, shall fully vest and
     the restrictions on his restricted stock grants, if any, shall lapse on the
     effective date of such termination,

          (c) Executive shall be entitled to continue to receive all the
     perquisites, benefits, services and equipment described in ss. 2.6 and
     ss. 2.8 of this Agreement for two (2) years after the effective date of
     such termination or the cash equivalent of such perquisites, benefits, 
     services and equipment (to the extent that Post and Executive agree on such
     cash equivalent), and

          (d) Executive shall receive all the perquisites and benefits to which
     he has a right to receive independent of this Agreement under the terms and
     conditions of the plans and programs under which such perquisites and
     benefits were granted to Executive.

          4.3. Termination as a Result of a Death or Disability Termination. If
Executive's employment under this Agreement is terminated as a result of Death
or Disability Termination,

          (a) Executive (or at his death, his designated beneficiary, if any, or
     if none, his surviving spouse or, if none, his estate) shall be entitled to
     receive (i) any Base Salary which may be owed to Executive but which is
     unpaid as of the effective date of such termination, (ii) the Pro Rata
     Bonus, and (iii) a severance payment equal to his Total Annual Compensation
     for such year, and

          (b) Executive's unvested stock options shall fully vest on the
     effective date of such termination, and

          (c) all Executive's perquisites and benefits called for exclusively
     under the terms of this Agreement shall terminate as of the effective date
     of such termination, but all of Executive's perquisites and benefits to
     which he has a right independent of this Agreement shall remain in effect,
     if at all, exclusively under the terms and conditions of the plans and
     programs under which such perquisites and benefits were granted to
     Executive.

          4.4. Employee Benefit Plans and Incentive Compensation and Other
Compensatory Arrangements. Executive shall be eligible for such benefits, if
any, in addition to those described in Section 4.1, 4.2 and 4.3 upon his
termination of employment as payable under any employee benefit plans pursuant
to the terms and conditions set forth in such plans.


                                       -7-

<PAGE>   8



                                     ss. 5.

                                Change In Control

          5.1. Definition. A Change in Control under this Agreement shall mean
(A) a "change in control" of Post of a nature that would be required to be
reported in response to Item 6(e) of Schedule 14A for a proxy statement filed
under Section 14(a) of the Securities Exchange Act of 1934, as amended ("1934
Act") as in effect on June 1, 1998, (B) a "person" (as that term is used in
14(d)(2) of the 1934 Act) becomes the beneficial owner (as defined in Rule 13d-3
under the 1934 Act) directly or indirectly of securities representing 45% or
more of the combined voting power for election of directors of the then
outstanding securities of Post, (C) the individuals who at the beginning of any
period of two consecutive years or less (starting on or after June 1, 1998)
constitute Post's Board of Directors cease for any reason during such period to
constitute at least a majority of Post's Board of Directors, unless the election
or nomination for election of each new member of such Board was approved by vote
of at least two-thirds of the members of such Board then still in office who
were members of such Board at the beginning of such period, (D) the shareholders
of Post approve any dissolution or liquidation of Post or any sale or
disposition of 50% or more of the assets or business of Post, or (E) the
shareholders of Post approve a merger or consolidation to which Post is a party
(other than a merger or consolidation with Post LP, Services or a wholly-owned
subsidiary of Post, Post LP or Services) or a share exchange in which Post shall
exchange Post shares for shares of another corporation as a result of which the
persons who were shareholders of Post immediately before the effective date of
such merger, consolidation or share exchange shall have beneficial ownership of
less than 50% of the combined voting power for election of directors of the
surviving corporation following the effective date of such merger, consolidation
or share exchange.

          5.2. Effect of a Change in Control. If Executive's employment with
Post is terminated by Post or by Executive for any reason other than a For Cause
Termination or a Death or Disability Termination during the two (2) year period
immediately following a Change in Control, Post (on behalf of Post, Post LP and
Services) shall in lieu of any benefit under ss. 4 (i) promptly pay Executive
any Base Salary which may be owed to Executive but is unpaid as of the effective
date of such termination, (ii) promptly pay Executive the Pro Rata Bonus, (iii)
promptly pay Executive three (3) times the total of (a) Executive's Base Salary
and (b) the average of all his annual incentive payments, if any, for the three
(3) preceding calendar years; (iv) continue to make available to Executive all
the perquisites, benefits, services and equipment described in ss. 2.6 and
ss. 2.8 of this Agreement for three (3) years after the effective date of such
termination or the cash equivalent of such perquisites, benefits, services and
equipment (to the extent that Post and Executive agree on such cash equivalent),
(v) fully vest all of Executive's stock options and make such options
exercisable for the maximum permissible term under the terms of the plan under
which the options were granted or for two years, whichever is less, and (vi)
waive any restrictions on Executive's right to receive any restricted stock
which had been granted to Executive.

          5.3. Tax Protection. If Post determines that the payments, option
vesting, forfeiture lapses and other benefits called for under Section 5.2 will
result in Executive being subject

                                       -8-

<PAGE>   9



to an excise tax under Section 4999 of the Internal Revenue Code of 1986, as
amended (the "Code"), or if such an excise tax is properly and timely assessed
against Executive as a result of a Change in Control or if such a determination
is made and such a tax is assessed, Post (on behalf of Post, Post LP and
Services) shall make a Gross-Up Payment to Executive at the time his employment
terminates, if a determination is made that an excise tax is due at that time,
or at the time of such assessment, or at both such times, as appropriate. A
"Gross-Up Payment" means a payment to Executive which shall be sufficient for
Executive to pay (i) any such excise tax in full, (ii) any federal, state and
local income tax on the payment made to pay Executive's excise tax as well as
any additional excise tax on such payment and (iii) any interest or penalties
assessed by the Internal Revenue Service on Executive if Post failed to
determine and report to Executive and to the Internal Revenue Service the full
amount on which an excise tax was due at the time Executive's employment
terminated. Any determination under this Section 5.3 by Post shall be made in
accordance with Section 280(g) of the Code and any related regulations (whether
proposed, temporary or final) and any related Internal Revenue Service rulings
and any related case law.

                                     ss. 6.

                                  Miscellaneous

          6.1. Binding Effect. This Agreement shall inure to the benefit of and
shall be binding upon Executive and his executor, administrator, heirs, personal
representative and assigns, and upon Post, Post LP and Services and their
successors and assigns; provided, however, that Executive shall not be entitled
to assign or delegate any of his rights or obligations hereunder without the
prior written consent of Post, Post LP and Services.

          6.2. Construction of Agreement. No provision of this Agreement or any
related document shall be construed against or interpreted to the disadvantage
of any party hereto by any court or other governmental or judicial authority by
reason of such party having or being deemed to have structured or drafted such
provision.

          6.3. Governing Law. This Agreement shall be governed by and construed
in accordance with the laws of the State of Georgia.

          6.4. Survival of Agreements. All covenants and agreements made herein
shall survive the execution and delivery of this Agreement and the termination
of Executive's employment hereunder for any reason.

          6.5. Headings. The section and paragraph headings contained in this
Agreement are for reference purposes only and shall not affect in any way the
meaning or interpretation of this Agreement.


                                       -9-

<PAGE>   10



          6.6. Notices. All notices, requests, consents and other communications
hereunder shall be in writing and shall be deemed to be given when delivered
personally or mailed first class, registered or certified mail, postage prepaid,
in either case, addressed as follows:

         (a) If to Executive:

             Mr. John A. Williams
             4615 Northside Drive, N.W.
             Atlanta, Georgia  30327

         (b) If to Post, Post LP or Services:

             Post Properties, Inc.
             One Riverside
             4401 Northside Parkway
             Suite 800
             Atlanta, Georgia  30327

             with a copy to:

             Mr. Herschel M. Bloom
             King & Spalding
             191 Peachtree Street
             Atlanta, Georgia  30303-1763

          6.7. Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original, but all of which
together shall constitute one and the same instrument.

          6.8. Entire Agreement. This Agreement constitutes the entire agreement
of the parties with respect to the subject matter hereof and upon the Effective
Date, will supersede and replace all prior agreements, written and oral, between
the parties hereto or with respect to the subject matter hereof. This Agreement
may be modified only by a written instrument signed by each party hereto.


                                      -10-

<PAGE>   11


          IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the date first above written.


                                POST PROPERTIES, INC.



                                By:  /s/
                                   --------------------------------------------

                                Title:  
                                      -----------------------------------------



                                POST APARTMENT HOMES, L.P.

                                By: Post GP Holdings, Inc., its General Partner


                                By:  /s/
                                   --------------------------------------------

                                Title:
                                      -----------------------------------------



                                POST SERVICES, INC.


                                By:  /s/
                                   --------------------------------------------

                                Title:  
                                      -----------------------------------------



                                EXECUTIVE

                                John A. Williams
                                -----------------------------------------------
                                John A. Williams


                                      -11-