John Duffy
John Duffy may refer to:
Sportspeople
- John Duffy (footballer, born 1886), English football centre half for Bradford City
- John Duffy (footballer, born 1922), Scottish football right back for Clyde and Norwich
- John Duffy (footballer, born 1929), Scottish football wing half for Celtic, Arbroath and Southend
- John Duffy (footballer, born 1943), Scottish football wing half for Raith, Dunfermline, Darlington and Australian clubs
- John Duffy (Gaelic footballer), Gaelic football player
- John Duffy (rugby league), rugby league player
- John Duffy (soccer), American soccer player
Others
- John Duffy (composer), American composer
- John Duffy (economist), American economist
- John Duffy (mobster), American gang member, member of the North Side Gang
- John Duffy (writer), Canadian writer and political strategist
- John Duffy and David Mulcahy, the Railway Rapists, British rapists and murderers
- John A. Duffy, American bishop
- John F. Duffy, legal academic
- John Gavan Duffy, Australian politician
- John J. Duffy, American Medal of Honor recipient
- John J. Duffy Jr., American criminal defense attorney
- John Duffy (medical historian), University professor & author of several books on U.S. medical history