Jack O'Brien
Jack O'Brien may refer to:
Sports
- Jack O'Brien (American football), American football player
- Jack O'Brien (catcher), Major League Baseball player
- Jack O'Brien (cricketer), New Zealand cricketer
- Jack O'Brien (footballer, born 1887), Australian rules footballer for Essendon and Fitzroy
- Jack O'Brien (footballer, born 1893), Australian rules footballer for South Melbourne
- Jack O'Brien (footballer, born 1898), Australian rules footballer for Essendon and Footscray
- Jack O'Brien (footballer, born 1906), Australian rules footballer for South Melbourne and Hawthorn
- Jack O'Brien (outfielder), American baseball player
- Jack O'Brien (wrestler), American-born Mexican professional wrestler
- Jack O'Brien (rugby union), New Zealand international rugby union player
- Philadelphia Jack O'Brien, American boxer, former light heavyweight boxing champion of the world
- Young Jack O'Brien, lightweight boxer from Pennsylvania
Others
- Jack O'Brien (director), American theatre director and producer
- Jack O'Brien (jazz pianist), big band pianist and songwriter
- John B. O'Brien, American actor and film director
- Jack O'Brien, founder of American website of Cracked.com