Borshuk started boxing at a young age, and started competing as an amateur boxer at the age of 15 on 19 June 1931 in Windsor against Henry Ule. When he was 18 years old in 1934 he became professional. In May 1941 he became national champion beating Terrence Warrington after a 12-round match. During his career he had 103 fights, winning 65 of them (31 losses, 7 draws).