EXHIBIT 99.1
 
                                REVOCABLE PROXY
                             PEOPLES BANK OF UNITY
                        SPECIAL MEETING OF SHAREHOLDERS
                                APRIL 18, 1997
 
  The undersigned hereby appoints         ,          and          of Peoples
Bank of Unity ("Peoples") or any successors, with full powers of substitution,
to act as attorneys and proxies for the undersigned to vote all shares of the
common stock of Peoples ("Peoples Common Stock") which the undersigned is
entitled to vote at the Special Meeting of Shareholders (the "Meeting"), to be
held at Alcoma Golf Club, located at 6770 Saltsburg Road, Pittsburgh,
Pennsylvania, on April 18, 1997, at 2:00 p.m. Eastern Standard Time and at any
and all adjournments thereof, as follows:
 
  1. To consider and vote upon the approval of the Agreement and Plan of
Reorganization and related Agreement and Plan of Merger (collectively the
"Agreement") among Peoples, S&T Bancorp, Inc. ("S&T") and S&T Bank which
provides for the merger of Peoples with and into S&T Bank, a wholly owned
subsidiary bank of S&T (the "Merger"), pursuant to which immediately prior to
the Effective Date, each share of Peoples Common Stock, par value $10.00 per
share, will be converted and exchanged for 26.25 shares of common stock of
S&T, par value $2.50 per share, and cash in lieu of any fractional share
determined in accordance with the terms of the Agreement; and
 
  2. To transact such other business as may properly come before the meeting
or any adjournment thereof.
 
  Only shareholders of record as of the close of business on         , 1997
are entitled to notice of and to vote at such meeting or any adjournment
thereof.
 
            FOR [_]             AGAINST [_]            ABSTAIN [_]
 
   THE BOARD OF DIRECTORS RECOMMENDS A VOTE "FOR" APPROVAL OF THE AGREEMENT.

 
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THIS PROXY WILL BE VOTED AS DIRECTED, BUT IF NO INSTRUCTIONS ARE SPECIFIED,
THIS PROXY WILL BE VOTED FOR APPROVAL OF THE AGREEMENT. IF ANY OTHER BUSINESS
IS PRESENTED AT THE MEETING, INCLUDING MATTERS RELATING TO THE CONDUCT OF THE
MEETING, THIS PROXY WILL BE VOTED BY THOSE NAMED IN THIS PROXY IN ACCORDANCE
WITH THE DETERMINATION OF A MAJORITY OF THE BOARD OF DIRECTORS. AT THE PRESENT
TIME, THE BOARD OF DIRECTORS KNOWS OF NO OTHER BUSINESS TO BE PRESENTED AT THE
MEETING.
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               THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS
 
  Should the undersigned be present and elect to vote at the Meeting or at any
adjournment thereof and after notification to the Secretary of Peoples at the
Meeting of the shareholder's decision to terminate this proxy, then the power
of said attorneys and proxies shall be deemed terminated and of no further
force and effect.
 
  The undersigned acknowledges receipt from Peoples prior to the execution of
this proxy of the Notice of Meeting and the Proxy Statement/Prospectus. The
undersigned hereby revokes any and all proxies heretofore given with respect
to the undersigned's shares of Peoples Common Stock.
 
                                          Dated:         , 1997
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                                          PRINT NAME OF SHAREHOLDER
 
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                                          SIGNATURE OF SHAREHOLDER
 
                                          Please sign exactly as your name
                                          appears on this card. When signing as
                                          attorney, executor, administrator,
                                          trustee or guardian, please give your
                                          full title. If shares are held
                                          jointly, each holder should sign.
                                          
  PLEASE COMPLETE, DATE, SIGN AND MAIL THIS PROXY PROMPTLY IN THE ENCLOSED
POSTAGE-PREPAID ENVELOPE.