William Wagner may refer to:
- William Wagner (land surveyor) (1820–1901), Polish-born Canadian land surveyor
- William Wagner (actor) (1883–1964), American character actor
- William Wagner (philanthropist) (1796–1885), American philanthropist and natural history museum founder in Philadelphia
- William Wagner (physician), German American physician and revolutionary
- Kenny Wagner (William Kenneth Wagner, 1903–1958), Mississippi bootlegger
- William G. Wagner, Williams College faculty member and former interim president
- Bull Wagner (William George Wagner, 1887–1967), pitcher in Major League Baseball
- Wolfe Wagner (William Wolfe Wagner, died 1937), Irish Anglican clergyman
- Bill Wagner (1894–1951), American baseball catcher
- Bill Wagner (software), American software developer
- Bill Wagner III, Arizona politician
- Stanley Wagner (winemaker) (Stanley "Bill" Wagner), early American vintner
- Guillermo Wagner Granizo (Guillermo "Bill" Wagner Granizo), American ceramic tile artist
- Billy Wagner (William Edward Wagner, born 1971), MLB pitcher