John Gallagher Montgomery (June 27, 1805 – April 24, 1857) was an American lawyer from Danville, Pennsylvania. He represented Pennsylvania in the U.S. Congress briefly in 1857. John Montgomery was born in Northumberland, Pennsylvania. He studied under a private tutor, and graduated from Washington College (now Washington and Jefferson College) in Washington, Pennsylvania, in 1824. He studied law, was admitted to the bar in 1827 and commenced practice in Danville. He was a member of the Pennsylvania House of Representatives in 1855.