William Fitzgerald may refer to:
- William FitzGerald (bishop) (1814–1883), Anglican bishop, first of Cork, Cloyne and Ross and then of Killaloe and Clonfert
- William Fitzgerald (Bishop of Clonfert and Kilmacduagh) (died 1722), Anglican bishop in Ireland
- William FitzGerald (Irish judge) (1906–1974), Irish lawyer and judge
- William Fitzgerald (Tennessee politician) (1799–1864), United States Representative from Tennessee
- William FitzGerald, 2nd Duke of Leinster (1749–1804), Irish liberal politician and landowner
- William FitzGerald, 13th Earl of Kildare (died 1599), Irish nobleman
- William FitzGerald-de Ros, 22nd Baron de Ros (1797–1874), British Lord and general
- William Fitzgerald, Niagara Falls daredevil who used the alias Nathan Boya
- William Charles Fitzgerald (1938–1967), United States Navy officer who was killed in action during the Vietnam War
- William F. Fitzgerald (1846–1903), California Attorney General and a California Supreme Court justice
- William H. G. FitzGerald (1909–2006), U.S. Ambassador to Ireland, 1992–1993
- William Henry Fitzgerald (1849–1922), Wisconsin State Assemblyman
- William J. Fitzgerald (1887–1947), U.S. Representative from Connecticut
- William James Fitzgerald (jurist) (1894–1989), Irish jurist; Chief Justice of the Supreme Court of Palestine during the time of the British Mandate
- William James Fitzgerald (Kansas politician) (1861–1937), Lieutenant Governor of Kansas
- William Patrick Fitzgerald (1864–1938), Australian politician
- William S. Fitzgerald (1880–1937), American politician
- William Fitzgerald (educationalist) (1838–1920), New Zealand teacher and educationalist
- William T. Fitzgerald (1858–1939), U.S. Representative from Ohio
- William Thomas Fitzgerald (1759–1829), British poet
- William Vincent Fitzgerald (1867–1929), Australian botanist
- William B. Fitzgerald (1914–1970), Michigan politician
- William B. Fitzgerald Jr. (1942–2008), American politician in Michigan
- Billy Fitzgerald (William James Fitzgerald), Canadian field lacrosse player