<PAGE>   1





                                                                  EXHIBIT 10.12c

                                THIRD AMENDMENT
                                       TO
                     AMENDED AND RESTATED CREDIT AGREEMENT


         This Third Amendment to Amended and Restated Credit Agreement (this
"Amendment"), made and entered into as of June 13, 1997, by and among
O'Sullivan Industries, Inc., a Delaware corporation ("Industries"), O'Sullivan
Industries Holdings, Inc., a Delaware corporation ("Holdings"; Industries and
Holdings are sometimes referred to hereinafter individually and collectively as
"Borrower"), O'Sullivan Industries - Virginia, Inc., a Virginia corporation and
wholly-owned subsidiary of Industries, as a guarantor and a letter of credit
account party ("O'Sullivan - Virginia"), O'Sullivan Industries International,
Ltd., a Barbados corporation ("O'Sullivan International"; O'Sullivan - Virginia
and O'Sullivan International are sometimes referred to hereinafter individually
and collectively as "Guarantor"), The Boatmen's National Bank of St. Louis, a
national banking association, as a lender ("Lender") and The Boatmen's National
Bank of St. Louis, as agent ("Agent").

                                   Recitals:

A.       Borrower, O'Sullivan - Virginia, Agent and Lender are the current
         parties to that certain Amended and Restated Credit Agreement by and
         among Borrower, O'Sullivan - Virginia, Agent, Lender and Wachovia Bank
         of Georgia, N.A. ("Wachovia"), a national banking association, as a
         lender, effective November 22, 1994, as amended by that First
         Amendment thereto, dated as of May 15, 1995, that Second Amendment
         thereto, dated as of December 29, 1995, and that certain letter from
         Borrower to Lenders, dated June 24, 1996 (as it may be further
         amended, restated, extended, renewed, replaced, or otherwise modified
         from time to time, the "Loan Agreement") pursuant to which certain
         credit facilities were extended to Borrower.

B.       This Amendment is being entered into contemporaneously with that
         certain Assignment and Acceptance (the "Assignment") among Wachovia
         and Lender.

C.       Borrower, Guarantor, Agent and Lender desire, upon the terms and
         conditions set forth herein, to amend the Loan Agreement as provided
         herein.

         In consideration of the mutual covenants and promises contained herein
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, Borrower, Guarantor, Agent and Lender agree as
follows:

1.       DEFINITIONS.  All capitalized terms used and not otherwise defined
herein shall have the meanings given them in the Loan Agreement.  Section and
Exhibit references are to Sections and Exhibits of the Loan Agreement unless
otherwise indicated.

2.       EFFECTIVE DATE OF THIS AMENDMENT.  This Amendment is effective upon
the satisfaction of the conditions in Section 4 of this Amendment.

3.       AMENDMENT TO LOAN AGREEMENT. 


                                  Page 1 of 6
<PAGE>   2

          3.1.      AGGREGATE REVOLVING COMMITMENT; EXHIBIT 2.1.1.  The
"Aggregate Revolving Commitment" set forth in Section 2.1.2, is reduced from
$30,000,000 to $25,000,000.  Exhibit 2.1.1 is replaced with Exhibit 2.1.1.
attached hereto.

         3.2.      ULTIMATE REVOLVING MATURITY DATE.  The words "December 31,
1997" in the first sentence of Section 2.1.1 are deleted and replaced with the
following: "February 28, 2000".

         3.3.    STANDBY LC FEE.  Section 4.2 is deleted and replaced with
the following:

                 4.2.     STANDBY LC FEE.  Borrower shall pay to Agent for the
         account of Lenders in accordance with their Prorata Shares a "Standby
         LC Fee" for each standby Letter of Credit issued by Agent (exclusive
         of the IRB Letter of Credit) that shall be calculated by applying the
         quarterly equivalent of .75% to the aggregate undrawn amount of such
         Letter of Credit.  The Standby LC Fee for each such Letter of Credit
         shall be payable in advance on its issuance date and on the first day
         of each calendar quarter beginning thereafter while it is outstanding.

         3.4.    IRB LC FEE.  Section 4.4 is deleted and replaced with the
following:

                 4.4.     IRB LC FEE.  Borrower shall pay to Agent for the
         account of Lenders in accordance with their Prorata Shares an "IRB LC
         Fee" for the IRB Letter of Credit issued by Agent that shall be
         calculated by applying the quarterly equivalent of .75% per annum to
         the aggregate undrawn amount thereof; provided however, that for each
         day on which an Event of Default exists and is continuing, the rate at
         which the IRB LC Fee shall accrue shall be the quarterly equivalent of
         3% per annum of the aggregate undrawn amount of the IRB Letter of
         Credit.  The IRB LC Fee for the IRB Letter of Credit shall be payable
         on the first day of each calendar quarter while it is outstanding.

         3.5.    USE OF PROCEEDS.  Section 13.1 is deleted and replaced with
the following:

                 13.1.    USE OF PROCEEDS.  Advances shall be used solely for
         working capital, plant expansion, purchases of outstanding equity
         securities of Holdings as permitted in Section 14.1.5. and other
         expenditures that are not prohibited herein and as the source for
         payment of Borrower's reimbursement obligations with respect to draws
         on Letters of Credit.

         3.6.    INVESTMENTS.  Section 14.1.5 is deleted and replaced with the
following:

                 14.1.5.  Equity securities of Holdings which are purchased 
         for a Dollar amount not in excess of (i) during calendar year 1997,
         $15,000,000, and (ii) during calendar year 1998, $5,000,000 plus the
         unexpended amount allowed for calendar year 1997; in determining the
         Dollar amount expended for such securities, the Dollar amount expended
         to purchase such securities which have been reissued to employees of
         Holdings or its Subsidiaries pursuant to the O'Sullivan Industries
         Holdings, Inc. Stock Purchase Program and the O'Sullivan Industries
         Holdings, Inc. Profit Sharing Plan, shall not be considered.

         3.7.    DEFINED TERMS.

                 13.1.   INTEREST HEDGE OBLIGATIONS.  The following definition
         is added, in alphabetical order, to the Glossary and Index of Defined
         Terms which is attached to the Loan Agreement as Appendix 1.1:




                                  Page 2 of 6
<PAGE>   3


                 "Interest Hedge Obligations": any obligations of
                 Borrower to Agent or any Lender under any ISDA interest rate
                 and currency exchange agreement, master agreement, or similar
                 agreement between Borrower and Agent or any Lender under which
                 the exposure of Borrower to fluctuations in interest rates is
                 effectively limited, whether in the form of one or more
                 interest rate cap, collar, or corridor agreements, interest
                 rate swaps, currency or equity swaps, forward contracts,
                 foreign exchange contracts or the like, or options therefor.

                 13.1.    LOAN OBLIGATIONS.  The definition of "Loan
         Obligations" in the Glossary and Index of Defined Terms which is
         attached to the Loan Agreement as Appendix 1.1 is deleted and replaced
         with the following definition:

                 "Loan Obligations": all of Borrower's Indebtedness owing to
                 Agent or Lenders under the Loan Documents, whether as
                 principal, interest, fees or otherwise, all reimbursement
                 obligations of Borrower to Agent or Lenders with respect to
                 Letter of Credit Exposure, and all other obligations
                 (including but not limited to obligations for the payment of
                 money) and liabilities of Borrower to Agent or Lenders under
                 the Loan Documents and all Interest Hedge Obligations (in each
                 case including all extensions, renewals, modifications,
                 rearrangements, restructures, replacements and refinancings of
                 the foregoing, whether or not the same involve modifications
                 to interest rates or other payment terms), whether now
                 existing or hereafter created, absolute or contingent, direct
                 or indirect, joint or several, secured or unsecured, due or
                 not due, contractual or tortious, liquidated or unliquidated,
                 arising by operation of law or otherwise, including but not
                 limited to the obligation of Borrower to repay future advances
                 by Agent or Lenders, whether or not made pursuant to
                 commitment and whether or not presently contemplated by
                 Borrower, Agent or Lenders in the Loan Documents.

4.       CONDITIONS TO EFFECTIVENESS OF THIS AMENDMENT.  As conditions
precedent to the effectiveness of this Amendment, Borrower or Guarantor, as the
case may be, shall, unless waived in writing by Agent, furnish or cause to be
furnished to Agent the following (in the case of documents to be delivered, all
in form and substance satisfactory to Agent):

         4.1.    AMENDMENT.  This Amendment, duly executed on behalf of
Borrower and Guarantor.

         4.2.    ASSIGNMENT.  The Assignment, duly executed on behalf of
Wachovia, Borrower and O'Sullivan - Virginia.

         4.3.    NOTE.  An amended and restated Note of Borrower, of even date
herewith, in the principal amount of $25,000,000, payable to the order of the
Boatmen's and otherwise in form acceptable to Boatmen's and Agent.

         4.4.    GUARANTY OF O'SULLIVAN INTERNATIONAL.  An unlimited,
unconditional guaranty of the Loan Obligations, duly executed on behalf of
O'Sullivan International.

         4.5.    CERTIFICATE OF SECRETARY.  A Certificate of the Secretary of
each Borrower and each Guarantor certifying (i) that the copies of its articles
or certificate of incorporation and bylaws, with all amendments thereto,
delivered to Agent in connection with the initial loan closing are accurate and
complete and there have been no further amendments thereto, (ii) the
resolutions adopted by its Board of Directors authorizing the execution,
delivery and performance of this Amendment, the Assignment, the amended and
restated Note and related documents (collectively, the "Amendment Documents")
by it, and


                                  Page 3 of 6
<PAGE>   4


(iii) the names, titles, incumbency and true signatures of the corporate
officers who are authorized to sign the Amendment Documents on its behalf.

         4.6.     AMENDMENT FEE.  Borrower shall pay to Agent, for the ratable
benefit of Lenders, a non-refundable amendment fee of $28,600.

5.       GOOD STANDING CERTIFICATES.  Borrower agrees that Borrower shall
deliver or cause to be delivered to Agent, within 30 days of the date of this
Amendment, certificates of good standing of each Borrower and each Guarantor in
the states of incorporation and qualification of each Borrower and each
Guarantor, respectively, issued by the Secretary of State of such states and
that Borrower's failure to deliver cause to be delivered such good standing
certificates by such date shall constitute an Event of Default.

6.       REPRESENTATIONS AND WARRANTIES OF BORROWER AND GUARANTOR.  Each
Borrower and each Guarantor each hereby represents and warrants to Agent and
Lender that (i) no consents are necessary from any third parties in connection
with its execution, delivery or performance of the Amendment Documents to which
it is a party, (ii) the Amendment Documents to which it is a party constitute
the legal, valid and binding obligations of it, enforceable against it in
accordance with their terms, except to the extent that the enforceability
thereof against it may be limited by bankruptcy, insolvency, fraudulent
conveyance, reorganization, moratorium or similar laws affecting the
enforceability of creditors' rights generally or by equitable principles of
general application (whether considered in an action at law or in equity),
(iii) except as disclosed on the disclosure schedule attached to the Loan
Agreement as Exhibit 11 and the disclosure schedule attached to this Amendment
as Exhibit 4, all of the representations and warranties contained in Section
11, as amended by this Amendment, are true and correct in all material respects
with the same force and effect as if made on and as of the date of this
Amendment, except that with respect to the representations and warranties made
regarding financial data in Section 11.11, such representations and warranties
are hereby made with respect to the most recent Financial Statements and other
financial data (in the form required by the Loan Agreement) delivered by
Borrower as required by the Loan Agreement, and (iv) there exists no Default or
Event of Default under the Loan Agreement, as amended by this Amendment.

7.       EFFECT ON LOAN DOCUMENTS.  Except as specifically amended by the
Amendment Documents, the Loan Documents shall remain in full force and effect
and are hereby ratified and confirmed in all respects.  The execution, delivery
and effectiveness of the Amendment Documents shall not operate as a waiver of
any right, power or remedy of Lenders or Agent under the Loan Documents, nor
constitute a waiver of any provision of the Loan Documents except as
specifically set forth herein.  Upon the effectiveness of this Amendment, each
reference in the Loan Agreement to "the Agreement", "hereunder", "hereof",
"herein", or words of like import, shall mean and be a reference to the Loan
Agreement, as amended hereby.

8.       REAFFIRMATION.  Each Borrower and each Guarantor each hereby ratifies,
affirms, acknowledges, and agrees that the Loan Agreement (as amended by this
Amendment) represents its valid, enforceable and collectible obligation, except
to the extent that the enforceability thereof against it may be limited by
bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium or
similar laws affecting the enforceability of creditors' rights generally or by
equitable principles of general application (whether considered in an action at
law or in equity), and it further acknowledges that there are no existing
claims, defenses, personal or otherwise, or rights of setoff whatsoever known
to it with respect to any of the Loan Documents.

9.       GOVERNING LAW.  The Amendment Documents shall be governed by and
construed in accordance with the laws and decisions of the State of Missouri
without giving effect to the choice or conflicts of law principles thereunder.


                                  Page 4 of 6
<PAGE>   5


10.      SECTION TITLES.  The section titles contained in this Amendment are
and shall be without substance, meaning or content of any kind whatsoever and
are not a part of the agreement between the parties hereto.

11.      COUNTERPARTS; FACSIMILE TRANSMISSIONS.  This Amendment may be executed
in one or more counterparts and on separate counterparts, each of which shall
be deemed an original, but all of which together shall constitute one and the
same instrument.  Signatures to this Amendment may be given by facsimile or
other electronic transmission, and such signatures shall be fully binding on
the party sending the same.

12.      INCORPORATION BY REFERENCE.  Agent, Lender, Borrower and Guarantor
hereby agree that all of the terms of the Loan Documents are incorporated in
and made a part of this Amendment by this reference.

13.      STATUTORY NOTICE.  The following notice is given pursuant to Section
432.045 of the Missouri Revised Statutes; nothing contained in such notice will
be deemed to limit or modify the terms of the Loan Documents or this Amendment:

         ORAL AGREEMENTS OR COMMITMENTS TO LOAN MONEY, EXTEND CREDIT OR TO
         FORBEAR FROM ENFORCING REPAYMENT OF A DEBT INCLUDING PROMISES TO
         EXTEND OR RENEW SUCH DEBT ARE NOT ENFORCEABLE.  TO PROTECT YOU
         (BORROWER(S) AND GUARANTOR(S) AND US (CREDITOR) FROM MISUNDERSTANDING
         OR DISAPPOINTMENT, ANY AGREEMENTS WE REACH COVERING SUCH MATTERS ARE
         CONTAINED IN THIS WRITING, WHICH IS THE COMPLETE AND EXCLUSIVE
         STATEMENT OF THE AGREEMENT BETWEEN US, EXCEPT AS WE MAY LATER AGREE IN
         WRITING TO MODIFY IT.

BORROWER, GUARANTOR, AGENT AND LENDER HEREBY AFFIRM THAT THERE IS NO UNWRITTEN
ORAL CREDIT AGREEMENT BETWEEN ANY OF THEM WITH RESPECT TO THE SUBJECT MATTER OF
THIS AMENDMENT.



                     [REST OF PAGE IS INTENTIONALLY BLANK]


                                  Page 5 of 6
<PAGE>   6


     IN WITNESS WHEREOF, this Amendment has been duly executed as of the day
and year first above written.

                              O'SULLIVAN INDUSTRIES, INC.
        
                              By:     /s/Terry L. Crump
                                      Chief Financial Officer

                              O'SULLIVAN INDUSTRIES HOLDINGS, INC.

                              By:     /s/Terry L. Crump
                                      Chief Financial Officer

                              O'SULLIVAN INDUSTRIES - VIRGINIA, INC.

                              By:     /s/Terry L. Crump
                                      Chief Financial Officer

                              O'SULLIVAN INDUSTRIES INTERNATIONAL, LTD.

                              By:     /s/ Daniel F. O'Sullivan
                                      Chairman

                              THE BOATMEN'S NATIONAL BANK OF ST. LOUIS, AS AGENT

                              By:     /s/Mary E. Garrity
                                      Vice President



                                  Page 6 of 6