Under coach and close friend Malcolm Arnold, Jackson started out as a promising decathlete before switching to high hurdles. He won gold at the 1986 World Junior Championships and he soon switched to the senior ranks. Following a silver medal in the 1986 Commonwealth Games, he won the 110m hurdles silver at the 1988 Olympic Games behind Roger Kingdom. Although his career as an active competitor in the event would last a further fifteen years, the last ten of these as world record holder, and see him twice crowned World Champion, twice Commonwealth Champion and four times European Champion, this would remain his only Olympic medal of any colour. In 1992 he eased through his first round heat in 13.10 s (which proved faster than the Gold-medal winning time) but was restricted by an injury he picked up during the next round and could only finish seventh in the final, and in 1996 he came fourth and in 2000, fifth.