Diarmuid O'Hegarty was an Irish revolutionary and civil servant.
Born in Cork, O'Hegarty was prominent in the re-organisation of the Irish Volunteers after the 1916 Easter Rising. He was vice-commandant of the Irish Republican Army's 1st Dublin Brigade and became IRA Director of Organisation in 1920.
Supportive of the Anglo-Irish Treaty, in September 1922, following the death of Michael Collins, he was appointed commandant general, a member of the Army Council, and Director of Intelligence of the National Army
In March 1923, he was appointed Secretary to the Executive Council of the Irish Free State.