 Thornhill was first selected for the Munster team for the 1942 Railway Cup final.Lining out at full-back against Leinster, he ended the game with his first Railway Cup medal after the 4-09 to 4-05 victory.It was the first of three successive winners' medals for Thornhill, as he was also included on the team for the final victories over Leinster in 1943 and Connacht in 1944.