Trained by hall of fame trainer Emanuel Steward, he conquered the WBO world Middleweight championship knocking out John Mugabi in one round in 1991, and the WBC's version by knocking out Julian Jackson in five rounds in 1993.
McClellan went up in weight to challenge world Super-Middleweight champion Nigel Benn in London on February 25 of 1995. Televised to the United States by Showtime, the fight had a tragic ending, as McClellan, after dropping Benn out of the ring in round one and once again in round eight, took a knee in round ten and was counted out, collapsing in his corner and losing consciousness.
McClellan recovered his consiousness, but he lost his eyesight and his ability to walk. Sports Illustrated ran an article about the fight and it's outcome one week after the fight. McClellan's family flew to be by his side, and later on, he was flown back to his home country.
He has recently recovered some ability to walk, being helped by a cane, but he has not recovered his eyesight. His three sisters, more particularly Lisa McClellan, are responsible for his care nowadays. He has been the honoree at numerous banqueets and award ceremonies, and fellow boxing world champion Roy Jones Jr, often pointed as a possible rival during the 1980s, set up a foundation to help McClellan.
McClellan's record as a professional boxer was 31 wins and 3 losses with 29 wins by knockout.