In his earlier life Kilroy was a District Councillor for the Belmullet area and a member of the Belmullet Board of Guardians representing Sinn Féin. He was also Captain of the Ballyglass Compay of the Irish Volunteers and later Adjutant of the 7th Battalion Belmullet and was captured after the burning of the Ballyglass Coast Guard Station in August 1920. He was interned in Galway, and in Portland and Dartmoor until January 1922. He took the Anti-Treaty side in the subsequent Irish Civil War and was a member of the 5th Brigade of the 4th Western Division comprising Erris and Achill and North West Mayo. He was captured near Westport in November 1922 while serving with a Flying Column there and was interred in Harepark camp until 1924.