At the Junior World Championships 1992 Haughton won with the Jamaican relay silver. The following year he took part in the first major championships of the adult class. At the World Athletics Championships in Stuttgart in 1993, he was sixth in the second 400-meter run in 45.63. Two years later at the 1995 World Championships in Gothenburg Haughton ran the fastest race of his career; in 44.56 seconds he won the bronze medal behind Americans Michael Johnson and Butch Reynolds. The squadron took second place behind the U.S. season.
At the 1996 Olympics in Atlanta Haughton appeared only in the relay and won bronze behind the seasons from the United States and the United Kingdom. In 1997 Haughton went to at the major championships only in the relay at the World Indoor Championships he won silver behind the relay from the USA, at the 1997 World Championships bronze behind the United States and the United Kingdom. In Kuala Lumpur at the 1998 Commonwealth Games Haughton was in the singles final best Jamaicans in 45.49 seconds he ran to sixth place. The Jamaican relay won ahead of England and Wales, as the best runners of the United Kingdom divided up on the two scales.
Haughton won the 1999 at the Pan American Games in Winnipeg gold in 44.59 seconds ahead of Danny McCray from the U.S. and the Mexican Alejandro Cárdenas. The Jamaican relay was successful. A month later at the 1999 World Championships in Seville occupied Haughton in the final 7th place in 45.07 seconds, 0.76 seconds behind, he had Cárdenas, who also won bronze in Seville. The Jamaican relay won the bronze medal behind the United States and Poland.
At the 2000 Olympic Games in Sydney Haughton won bronze in 44.70 seconds behind Michael Johnson and Alvin Harrison. With the season he also won bronze. Also won two bronze medals at the World Championships Haughton, 2001 in Edmonton. In the individual decision he lay in 44.98 seconds behind Avard Moncur of the Bahamas and the German Ingo Schultz, but a hundredth of a second ahead of the best American Antonio Pettigrew. In the relay decision, the Americans won before the season of the Bahamas and Jamaica. 2004 was Haughton then again on the podium when he won the relay at the World Indoor Championships in Budapest.
Gregory Haughton studied in the U.S. at George Mason University. He had a competition weight of 79 kg at a height of 1.85 m.
Successes with the Season
- World Cup 1993: 7th place with Patrick O'Connor, Dennis Blake, Danny McFarlane, Haughton
- World Cup 1995: Silver with Michael McDonald, Davian Clarke, McFarlane, Haughton
- Olympic Games 1996: Bronze with McDonald, Roxbert Martin, Haughton, Clarke
- World Indoor Championships 1997: Silver with Linval Laird, McDonald, Dinsdale Morgan, Haughton
- World Championships 1997: Bronze with McDonald, Haughton, McFarlane, Clarke
- Commonwealth Games 1998: Gold with McDonald, Martin, Haughton, Clarke
- Pan American Games 1999: Gold with McDonald, Haughton, McFarlane, Clarke
- 1999 World Championships: Silver with McDonald, Haughton, McFarlane, Clarke
- Olympic Games 2000: Bronze with Michael Blackwood, Haughton, Christopher Williams, McFarlane
- 2001 World Championships: Bronze with Brandon Simpson, Williams, Haughton, McFarlane
- World Indoor Championships 2004: Gold with Haughton, Leroy Colquhoun, McDonald, Clarke
- 200 m: 20.64 s, May 19, 1996 Fairfax
- 400 m: 44.56 s, August 9, 1995, Gothenburg Hall: 45.66 s, February 11, 1995, Boston