He was a member of the Military Council of the Irish Republican Brotherhood, which planned and carried out the Rising of Easter 1916, outright rebellion against the world's biggest imperial power. During Easter week 1916, he was Commandant of the 4th Battalion of the Irish Volunteers and a signatory to the Proclamation of the Irish Republic. His severely depleted battalion held the strategic South Dublin Union until ordered to surrender.
He was executed by firing squad on 8 May 1916. 'an epic new series of books' - RTE Guide on 16Lives