William Wallace Irwin (1803 – September 15, 1856) was Mayor of Pittsburgh and a Whig member of the U.S. House of Representatives from Pennsylvania.

He became a member of the Allegheny County bar on May 6, 1828,[3] and by 1835 was serving as the president of the Western University's alumni association.

Irwin's first wife was Frances Everallyn Rose Irwin (April 1809–February 24, 1836), the niece of Illinois Supreme Court justice Theophilus W. Smith and aunt of bridge engineer Charles Shaler Smith.

His second wife was Sophia Arabella Bache, born November 14, 1815, at Philadelphia, Pennsylvania, and died on March 24, 1904.

She was the daughter of Richard Bache, Jr., who served in the Republic of Texas Navy and was elected as a Representative to the Second Texas Legislature in 1847, and Sophia Burrell Dallas, the daughter of Arabella Maria Smith and Alexander J. Dallas, an American statesman who served as the U.S. Treasury Secretary under President James Madison.