As Second lieutenant of F Company, 1st Battalion, Dublin Brigade, Irish Volunteers, during the Easter rising Diarmuid Ó Hegarty was in charge of barricades in Church St., Mary Lane, Mary's Abbey, and Jameson's distillery, an area which saw fierce fighting.
Having failed to identify the importance of their prisoner, in error the authorities released him early, on 18 May, to return to his family and job in the civil service.