In addition to excelling in swimming, Mary (Stewart) McIlwaine was a talented performer, appearing as the BC Lions mascot ‘Leo the Lion’ for home games at Empire Stadium during their early years in the CFL. Mary’s sister Helen (Stewart) Hunt was also inducted into the BC Sports Hall of Fame for swimming. They were both coached by fellow BC Sports Hall of Famer Howard Firby.

Before the age of seventeen, Mary held every Canadian freestyle and butterfly record in all distances up to 220 yards. She also held American records for the 100m and 100-yard butterfly in 1961-62.

Mary won a silver medal at the 1959 Pan American Games in Chicago in the 4x100m freestyle relay. Her sister Helen was on the same Canadian relay team.

She reached the finals in the 100m freestyle event at the 1960 Olympic Games in Rome. Four years later she was again a member of the 1964 Canadian Olympic team in Tokyo and reached the Olympic final of the 100m butterfly. At those same Games she also helped the Canadian 4x100m medley relay team to a sixth place finish.

At the 1962 British Empire and Commonwealth Games in Perth, Australia, Mary won gold in the 110-yard butterfly, bronze in the 110-yard freestyle, and a silver and bronze in the relay events. That same year she established world records for the 100m and 110-yard butterfly.

At the 1963 Pan American Games in Sao Paulo, Brazil, Mary won four silver medals in the 100m freestyle, 100m butterfly, and freestyle and medley relay events.

Perhaps Mary’s proudest accomplishment was winning the Velma Springstead Trophy in back-to-back years as Canada’s outstanding female athlete of the year in 1961 and 1962.