William DeWitt Mitchell (September 9, 1874–August 24, 1955) was U.S. Attorney General for the entirety of Herbert Hoover's Presidency.

Born in Winona, Minnesota, he received his undergraduate and law degrees from the University of Minnesota. After he was admitted to the Minnesota bar he began practicing law in St. Paul. Mitchell served as an infantry officer during the Spanish-American War and World War I. On June 4, 1925, he was appointed Solicitor General of the United States. President Hoover appointed him Attorney General of the United States on March 4, 1929, and he held that office until March 4, 1933. Mitchell then settled in New York City where he practiced law. He was named chairman of the Committee on Federal Rules of Civil Procedure, and chief counsel of the joint congressional committee investigating the attack on Pearl Harbor. He died in 1955, in Syosset, New York.