Dennis O'Brien
Dennis or Denis O'Brien may refer to:
- Dennis O'Brien (ice hockey), professional ice hockey player in the National Hockey League
- Dennis M. O'Brien, former speaker, PA House of Representatives, and member, 167th District
- Denis O'Brien, Irish entrepreneur, charman of Digicel
- Denis O'Brien (footballer), Australian footballer for Collingwood
- Denis O'Brien (police officer), veteran of the Easter Rising and the Irish Republican Army
- Denis O'Brien (politician), New York state attorney general
- Denis O'Brien (producer), co-founder of HandMade Films with George Harrison
- Denis Patrick O'Brien, English economist
- Denny O'Brien, American columnist, journalist and radio commentator
- G. Dennis O'Brien, former president of the University of Rochester