John Watson competed in the individual three-day eventing at the 1988 Seoul Olympic Games, achieving one of his lifetime ambitions in the sport following disappointment in 1976 when his horse, Cambridge Blue, suffered a freak accident in official training and he was forced to withdraw before taking to the field of play.

After the 1976 Olympics Watson won bronze in the 1977 European Eventing Championship, and in 1978 was second in the World Championships in the 3-day. In 1979 he led Ireland to the gold medal in the European Eventing Championship, dropping out of the medals in the jumping when he put a rail down, finishing fifth individually.

In Seoul, Watson was unfortunate when his horse, Tullyneaskey, crashed out at the 16th fence of the cross-country course, leaving Watson with a broken collar bone and forced to withdraw. Watson later recalled that competing in the Seoul Olympics fulfilled a cherished personal ambition of competing on the Olympic stage.