John O'Callaghan

John O'Callaghan may refer to:

• John O'Callaghan (Medal of Honor) (1850–1899), American soldier and Medal of Honor recipient
• John O'Callaghan (politician) (died 1913), 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 (writer) (1805–1883), Irish historian and writer
• John Cornelius O'Callaghan, vocalist and guitarist of The Maine

See also

• John Callaghan (disambiguation)