Gunnell started out in athletics as an accomplished long jumper and pentathlete before turning to the sprints and hurdling and is the only woman to have held the European, World, Commonwealth and Olympic 400 metre hurdles titles at the same time.
Gunnell won the 400m hurdles at the 1992 Summer Olympic Games in Barcelona. She set the world record in the same event when she won gold in the 1993 World Championships. This record was broken by Kim Batten in 1995. Her defence of her Olympic title in Atlanta in 1996 was cut short as she pulled up in one of her races, injured.