Day first joined the Canadian Equestrian Team in 1964, and in 1966 tied the record high jump of 7 feet 1 inch at the National Horse Show in New York. Day took gold in individual jumping at the 1967 Pan American Games.[2] Day was named Canada's Horseman of the Year three years running in 1966 through 1968.[2] In 1968, he was a member of Canada's gold-medal equestrian team at the Summer Olympics in Mexico City.[1] At 22 years of age, Day was the youngest member of the show jumping team.[3] In the 1972 Olympics in Munich he finished 4th individually, and a team 6th. In the 1976 Summer Olympics he competed in both the show jumping and three-day eventing competitions, coming in 15th individually and 5th team in the show jumping, and not finishing the three-day eventing competition, although the Canadian team came in 6th.[1]