William Ryan may refer to:
William Fitts Ryan (1922–1972), congressman from New York
William H. Ryan (1860–1939), U.S. Representative from New York
William H. Ryan, Jr., former Delaware County District Attorney and acting Pennsylvania Attorney General
William Ryan (53rd Congress) (1840–1925), represented New York's 16th District in the Fifty-third United States Congress
William Ryan (Irish politician) (1921–1994), Irish Fianna Fáil politician, senator 1961–1989
William Ryan, who operated Crest Communities prior to its acquisition in 1978 by Ryland Homes
William Ryan (film director), director of Reach the Rock and Flubber
William Ryan (geologist), proponent of the Black Sea deluge theory
William Ryan (psychologist), author of the 1971 book Blaming the Victim
William Ryan (sailor), Australian sailor
William Ryan (Canadian politician) (1887–1938), Canadian Member of Parliament
William Ryan (footballer), English professional footballer who played as a goalkeeper
William Patrick Ryan (1867–1942), Irish author and journalist
William F. Ryan (1907–1954), American checkers player