A metal worker by trade Thomas served as a regimental sergeant major in the maritime branch of the Royal Artillery during the Second World War.
He saw action in the Atlantic, Russian and Indian waters, and at one time survived the sinking of his ship by a Japanese submarine.
[3] Six rugby league footballers represented Wales XV (RU) while at rugby league clubs, they were; Tyssul Griffiths, Elwyn Gwyther, Gomer Hughes, Hugh Lloyd-Davies, Harold Thomas, and Leslie Thomas.
Harold Thomas played at second-row in Salford's 7–4 victory over Barrow in the 1938 Challenge Cup Final during the 1937–38 season at Wembley Stadium, London, in front of a crowd of 51,243.
Harold Thomas played at second-row in Salford's 7–10 defeat by Wigan in the 1938 Lancashire Cup Final during the 1938–39 season at Station Road, Swinton on Saturday 22 October 1938.