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 (1805–1883), Irish historian and writer
 * John Joseph O'Callaghan (1838–1905), Irish architect
 * John O'Callaghan (singer), vocalist and guitarist of The Maine
 * John O'Callaghan (American football) (born 1964), American football player in the 1987 Seattle Seahawks season