He turned professional shortly after winning his Olympic medal and he would go on to win British, Commenwealth and European titles in a short five-year career. In 1960 he fought Alphonse Halimi for the World Bantamweight title but lost on points in London, despite knocking down Halimi in the fifteenth round. In 1963 Gilroy fought fellow Belfast man and Olympic medallist John Caldwell in what is widely regarded as one of the greatest fights ever to be held in Ireland. Gilroy won when a cut to Caldwell's eye stopped him from carrying on. Gilroy immediately announced his retirement.