He was born at Mount Egerton in Victoria to miner James Stephen O'Reilly and Maria Ryan.
He was a smelter miner at Port Pirie, and was blacklisted after his involvement in a 1909 lockout.
He went to Broken Hill, where he worked under false names and became active in the Miners' Union.
He was active in the anti-conscription campaign for the 1916 conscription referendum and was on the 1917 strike committee; he also worked on the staff of the Labor Daily from 1924, having moved to Newcastle.
From 1931 to 1933 he was a Labor member of the New South Wales Legislative Council; he died at Newcastle in 1933.