On July 15, 2000, Barrett rose 5 times against future International Boxing Federation heavyweight champion Wladimir Klitschko, but ultimately was knocked out after 3 knockdowns in the 7th round.

After Klitschko injured his back, Barrett fought Hasim Rahman for the WBC interim title and lost by unanimous decision after 12 rounds.

Haye then beat Nicolai Valuev, who had beaten Monte by an eleventh round stoppage in October 2006, to win the WBA's share of the world heavyweight title.

On August 7, 2010, appearing ringside at a fight card at Aviator Arena in Brooklyn, New York, in a brief interview, Barrett confirmed his retirement from the ring and his intention to take a job offered to him in private industry.

[2] On August 21, 2010, Barrett entered the ring at The Prudential Center in Newark after IBF International heavyweight champion Tomas Adamek won a decision over Michael Grant.

However, after fighting to an eight round draw in Virginia with Charles Davis in January 2011, Barrett began training for a rematch with David Tua which was held in New Zealand.

[3] Barrett fought New Zealander Shane Cameron on July 5, 2012 with the winner becoming the number one contender to fight NZPBA title holder Sonny Bill Williams.