John O'Callaghan
John O'Callaghan may refer to:
- John O'Callaghan (Medal of Honor), American soldier and Medal of Honor recipient
- John O'Callaghan (politician), secretary of the United Irish League
- John O'Callaghan (musician), Irish musician and DJ
- Liam McCarthy and John D. O'Callaghan, BT Young Scientists of the Year and EU Young Scientists of the Year, 2009
- John Cornelius O'Callaghan, Irish historian and writer
- John Joseph O'Callaghan, Irish architect
- John O'Callaghan (singer), vocalist and guitarist of The Maine
- John O'Callaghan (American football), American football player in the 1987 Seattle Seahawks season