A very eccentric personality who is known to have enjoyed the nightlife, Benn had a record of 41 wins and 1 loss as an amateur boxer. He turned professional in 1987 with a win over Graeme Ahmed in Croydon. This win opened a streak of 22 consecutive knockout wins for The Dark Destroyer. The streak extended until 1989. Among the achievements reached by Benn during the knockout win streak were beating Fermin Chirino, winning the British commonwealth's Middleweight title with a win over Abdul Umaru, and retaining it against David Noel, brother of former world Lightweight champion Claude Noel. But then, he lost the title to Michael Watson, by a knockout in round six. With that, he also lost his record as an undefeated fighter.
His next fight, against Jorge Amparo, was the first fight abroad for Benn and also the first Nigel Benn bout to last the full distance, when he won a 10 round decision over Amparo in Atlantic City, New Jersey, United States. After two more wins, he got his first opportunity at a world championship, when he faced WBO world Middleweight champion Doug DeWitt in Atlantic City. Benn crowned himself world champion by knocking out DeWitt (who had lasted 12 rounds against Thomas Hearns) in round eight. His next defense came against former WBC world champion Iran Barkley (who beat Hearns twice). He knocked Barkley out in round one. Then, he lost the world title, when he got knocked out in round nine by countryman Chris Eubank.
In 1991, he beat Marvin Hagler's half brother, Robbie Sims, by a knockout in round seven, and then he embarked in another winning streak, which would reach ten wins in a row. He won the WBC's world Super Middleweight title with a knockout in round four of defending world champion Mauro Galvano, after having beaten his future conqueror and world champion Sugar Boy Malinga by a decision in ten. He retained his title against Nick Piper, Galvano and Lou Gent before engaging in a rematch with Eubank. While Benn's second longest winning streak came to a halt, he retained the world title with a twelve round draw against Eubank. Next came Henry Wharton and Juan Carlos Gimenez, both of whom lost on points to Benn for the world title.
Benn's next fight would change his life forever: World Middleweight champion Gerald McClellan, eager to move up in weight and become a two time world champion just like Benn had done years before, challenged Benn. The fight was shown to many countries worldwide, and in the United States it was carried by Showtime. It was an eagerly anticipated match-up with many boxing fans tuning in, and McClellan dropped Benn out of the ring in round one. In round eight, Benn was dropped again. Seemingly on the verge of losing his title, Benn kept on charging, however, making for what several magazines called one of the fights of the year. In round ten, McClellan suddenly went down on one knee and the referee counted him the ten seconds to end the bout while he was still on one knee. McClellan collapsed when he went back to his corner and the scene inside the ring went berzerk, so much that Benn did not know what was happening until he was being interviewed by Showtime's commentator Dr. Ferdie Pacheco. McClellan was taken out on a stretcher and with an oxygen mask out of the ring, and he lost consciousness on his way to the hospital. He wouldn't recover consciousness for a very long time.
Benn spent the night at the emergency room waiting for news from his ring foe. The following morning, the McClellan family arrived in London and Benn was by their side. McClellan survived, but he has been blind ever since, and he was paralyzed for a very long period of time. Recently, he began to walk with the help of a cane. The following week after the fight, an article about it was published by Sports Illustrated.
According to Benn's trainer, this fight took out all the fighting spirit from Benn. As it happens many times when a tragedy of this type happens to a boxer, Benn had an ordinary record after that bout. He retained the title by knocking out future world champion Vincenzo Niardiello, and then he won a non-title bout, but that turned out to be his last career win. He lost to Malinga by a 12 round decision to lose the WBC world title, and then he was given a chance at the WBO's world title, but he lost to Steve Collins by a knockout in round four, after breaking his ankle during their fight in Manchester. An immediate rematch was ordered, also in Manchester, and that time around, Benn lost by a knockout in round seven.
Benn, who is still quite a celebrity in England and who has been recently invited to many London nightclubs as a DJ, had a record of 42 wins, 5 losses and 1 draw, with 35 wins by knockout, in professional boxing.