Magill was the Amateur Boxing Association of England's Middleweight Champion in 1934 and 1935 and Light Heavyweight Champion in 1936. He won fights in Boston and New York in an Irish tour of the US in 1935, was European Police champion from 1931 to 1936 and won a bronze medal representing Northern Ireland at the 1934 British Empire Games. As the Irish Amateur Boxing Association governed the sport in Northern Ireland, he was considered ineligible to compete for both Great Britain at the Olympics and Ireland at the Olympics. In 1936, Magill defeated Richard Vogt, who as a German Army Captain in 1940 saved the life of an Irish Guardsman wounded in the Dunkirk evacuation because they both knew Magill.