William Kelly or Bill Kelly may refer to:
- Bill Kelly (American football) (1905–1931), American football player at the University of Montana and in the NFL
- Bill Kelly (American football, born 1947), American football player and coach
- Bill Kelly (outfielder), 19th-century American baseball player
- Bill Kelly (first baseman) (1898–1990), American baseball player
- Bill Kelly (politician), politician in Lapeer, Michigan
- Bill Kelly (rugby league) (1892–1975), New Zealand rugby league footballer and coach
- Bill Kelly (writer), American screenwriter
- Kenneth Kelly (1905–1984), nicknamed "Bill", American football player and coach, head coach at Central Michigan University, 1951–1966
- William Kelly (artist), American artist
- William Kelly (Bible scholar) (1821–1906), classicist and Biblical expositor
- William Kelly (inventor) (1811–1888), American inventor of a steel smelting process
- William Kelly (Labour politician) (1874–1944), British Labour politician
- William Kelly (New York state senator) (1807–1872), New York politician
- William Kelly (New Zealand politician) (1840–1907), New Zealand Member of Parliament
- William Kelly (senator) (1786–1834), American Senator from Alabama
- William McDonough Kelly (born 1925), political strategist and retired Canadian Senator
- William Moore Kelly (1827–1888), businessman and politician in New Brunswick
- William Osmund Kelly (1909–1974), mayor of Flint, Michigan
- Willie Kelly (politician) (1877–1960), Australian politician