William M. Donnelly (1885 – January 30, 1946) was a politician from the U.S. state of Michigan.
Donnelly, of Detroit, Michigan, was an unsuccessful Democratic candidate from Michigan's 1st congressional district in a contest for a seat in the U.S. House in three consecutive elections.
He lost all three to Republican Robert H. Clancy in 1926, 1928 and 1930 for the 70th, 71st and 72nd Congresses.
He was a member of the Michigan Democratic State Central Committee and a delegate to Democratic National Convention from Michigan in 1928 and 1944.
Donnelly was a member of Michigan House of Representatives from Wayne County 1st District, 1933–34.