John Watson was educated at Eton, later graduating from the Royal Agricultural College at Cirencester. He received his riding instructor’s certificate at Porlock in Somerset. Watson made the 1976 Olympic team but was unable to compete after a freak accident to his horse, Cambridge Blue, in the official training area, when it cut its leg after sinking into marshy ground. 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. Watson finally made the Olympic stage at Seoul in 1988 but in the cross-country section of eventing, his horse fell, and Watson broke his collarbone, causing him to withdraw from the competition.
Watson was the son of Sidney Watson, whose family home was Ballingarrane House in Clonmel, and who wrote Three Full Days, the history of Irish eventing. John Watson sold Ballinngarrane House in November 2000 and settled at Ballybolger Stud Farm in County Carlow.