William Birney (May 28, 1819 – August 14, 1907) was a professor, Union Army general during the American Civil War, attorney and author. An ardent abolitionist, he was noted for encouraging thousands of free black men to join the Union army. Birney was a son of prominent Southern abolitionist leader James G. Birney and the older brother of Civil War general David B. Birney. Another brother, James Birney, served as Lieutenant Governor of Michigan in 1860. A cousin, Humphrey Marshall was a U.S. Congressman and a general in the Confederate States Army.