John Duffy
John Duffy is the name of:
- John A. Duffy (1884–1944), American bishop
- John Duffy (soccer) (1905–1984), American soccer player
- John Duffy and David Mulcahy (both born 1959), the Railway Rapists, British rapists and murderers
- John Duffy (mobster) (died 1924), American gang member, member of the North Side Gang
- John Duffy (economist) (born 1964), American economist
- John J. Duffy, Jr. (born 1933), American Criminal Defense attorney
- John F. Duffy, legal academic
- John Duffy (rugby league) (born 1980), rugby league player
- John Gavan Duffy (1844–1917), Australian politician
- Jack Duffy (1926–2008), Canadian entertainer
- Jack Duffy (actor) (1882–1939), American film actor