On July 2, 1815, Representative-elect Amos Ellmaker (DR) of Pennsylvania's 3rd district resigned after being appointed and commissioned president judge of the Twelfth Judicial District of Pennsylvania, composed of the counties of Dauphin, Lebanon, and Schuylkill, and before the 14th Congress' first session began. A special election was held on October 10, 1815 to fill the vacancy left by his resignation.
Election results
Wallace took his seat on December 4, 1815 at the start of the 1st session of the 14th Congress.
References
Pennsylvania's 3rd congressional district special election, 1815 Wikipedia(Text) CC BY-SA