 He made his debut on 9 July 1933 when he lined out at full-back in Cork's 7-05 to 4-05 defeat of Clare but was left out of the team for the subsequent Munster final.Thornhill was recalled to the team for the 1934 Munster final against Waterford, but ended the game on the losing side after the 7-10 to 5-02 defeat.After a number of years of no association with the team, Thornhill was restored to the full-back berth for the 1937 Munster Junior Championship.