Gwynne left school early and began to train to originally be Jockey in Toronto. His talent as a boxer has been recognized and promoted. At the age of 19 he won the Canadian amateur flyweight championship in Ontario. In the same year he took part in the weight class bantamweight in the qualifiers for the Olympic Games. He won shortly afterwards the Canadian Amateur Bantamweight Championship and was admitted to the 1932 Olympic Games in Los Angeles, where he won the gold medal after a points victory against the German Hans Ziglarski.
Immediately after the Olympics Gwynne turned pro and won the 1935 Canadian professional bantamweight title, which he held until his retirement in 1939. Out of 41 fights he won 31, he lost eight, the other two ending in draws. He was inducted into the Canadian Boxing Hall of Fame and the Canadian Sports Hall of Fame.