William D. Ryan (1861 – November 17, 1949) was an American labor unionist.
Born in Illinois, Ryan moved with his family to Braidwood, Illinois in 1865. He became a breaker boy at a colliery, and joined the Knights of Labor, and then the United Mine Workers of America. In 1897, he was elected as secretary-treasurer of his local, and became a full-time organizer for the union. In 1908, he was elected as secretary-treasurer of the international union, but he left the union movement in 1909. He then worked as an arbitrator for the Southwestern Interstate Coal Operators' Association, as a safety commissioner for the United States Bureau of Mines, and briefly ran a family coal and grain company.
Ryan retired in 1935, and died in Kansas City, Missouri in 1949.