Shannon Smith began swimming competitively in 1972 at age eleven. She swam first with the Canadian Dolphin Swim Club and later, under BC Sports Hall of Fame coach Ron Jacks, for the Byng Swim Club and the New Westminster Hyacks Club. Throughout her career, Smith consistently shattered record after record.

During her career, Smith won a total of 34 Canadian open and age group medals. She was world-ranked in seven events between 1975-78. Over that time, Smith won numerous international meet medals in the 200m, 400m, and 800m freestyle events at meets all over the world including the US and Japanese nationals.

In 1976, at the Olympic Games in Montreal, Smith won a bronze medal in the 400m freestyle. That same year she won gold at the US national championships in the 800m freestyle.