Gary O’Toole competed in the men’s 100m breastroke, 200m breaststroke and 200m individual medley at the 1988 Seoul Olympic Games, becoming the first Irish athlete to compete at the Seoul Games when he entered the pool on the opening day of the swimming programme where he placed 18th in the 200 metres breaststroke. In the 100 metres breaststroke he swam a new Irish record of 1:05.34, which included a new Irish record for the 50-metre split, placing him 34th.

O’Toole had taken a year’s sabbatical from his medical studies to prepare for Seoul, basing himself in Wales where he had access to a 50-metre pool, and also spending 16 weeks in Florida in October-January (1991-92).

Following the Olympic Games, he established himself as one of Ireland’s leading swimmers: in 1989 he won silver at the European Championships in the 200-metre breaststroke and took gold in the same event at the World Student Games in Sheffield in 1991, the first times an Irish swimmer had won medals in major international competition. O’Toole also helped break five national relay records across both short course and long course.

He went on to compete at the 1992 Barcelona Olympics in the same three events.

Following his retirement from professional swimming, O’Toole has been a practising orthopedic surgeon and has been a contributor to RTE Sport’s Olympic swimming coverage.