[8] As a professional wrestler, Barnett made his in-ring debut in 2003 in the main event of New Japan Pro-Wrestling's annual January 4 Tokyo Dome Show, in a bout against IWGP Heavyweight Champion Yuji Nagata.
In January 2015, Barnett began working as a color commentator for NJPW's weekly program on America's AXS TV.
Barnett attended Ballard High School, where he excelled at wrestling, football, and also trained in judo, karate and Muay Thai.
Barnett had originally attended the University of Montana to play football for the school as a walk-on, but decided to pursue fighting instead.
They would share information, arrange a location, agree upon rules, and use improvised gloves, often fighting several times as well as training together.
He accepted the fight with less than two weeks notice while home for winter break after being contacted by organizer Matt Hume, his former high school wrestling coach, and won by submission via rear-naked choke in under three minutes.
[11][14] Barnett started training in catch wrestling and no-holds-barred with Hume's AMC Pankration team to prepare for his next fight.
[12] He would compile a 9–0 record with seven first-round stoppages and wins over future UFC Hall of Famer Dan Severn, Bobby Hoffman, John Marsh, and Bob Gilstrap twice.
Subsequent to his win over Hoffman, Barnett tested positive for banned substances and was given a warning by the Nevada State Athletic Commission.
He submitted Mark Hunt via kimura in the first round of the Openweight Grand Prix at Pride Critical Countdown Absolute.
Next, Barnett fought the Polish judo gold medalist Pawel Nastula at PRIDE 32, the organization's first show in the United States.
Barnett did not follow many other PRIDE veterans to the UFC because he desired to join an organization that included the top Heavyweight fighter in the world, Fedor Emelianenko.
Due to the positive drug tests, Barnett made a re-licensure appeal to the California State Athletic Commission (CSAC).
Michael J. DiMaggio, Barnett's attorney, was unable to attend the hearing because of travel problems, causing the third extension, which would have taken place February 22, 2010.
[40][41] In March 2018, Barnett was clear to fight and received a "public reprimand" instead of a suspension from USADA after it was determined that his failed test was the result of a contaminated supplement.
[42] On June 20, 2018, Barnett was granted his request to be released from UFC, claiming he does not trust the United States Anti-Doping Agency.
[47] Barnett began his career as a professional wrestler in the New Japan Pro-Wrestling (NJPW) organization, where he wrestled numerous matches in 2003 and 2004.
Although unsuccessful in that match,[48] Barnett formed a tag team with Perry Saturn and was undefeated in the following NJPW tour, Fighting Spirit 2003.
[49] In January 2015, Barnett began working as a color commentator for NJPW's weekly program on AXS TV.
Since the loss, he has been on a winning streak beating The Predator, Hitokui Yoshiki, Tank Abbott, Jon Andersen, Fonseca, Atsushi Sawada, Bob Sapp, Ultimate Mask, Tim Sylvia, Montanha Silva, Bobby Lashley and Hideki Suzuki.
In July at IGF Genome 16, he defeated Bobby Lashley with a cross armbreaker to advance to the finals of the title tournament.
[54] During the January 2017 Impact Wrestling tapings, Barnett unsuccessfully faced Bobby Lashley in an open challenge for the TNA World Heavyweight Championship.
[55] Barnett returned to IGF on April 5, 2017, defeating Shinichi Suzukawa on the promotion's inaugural Next Exciting Wrestling (NEW) event.
[61]: 52ː17 Barnett competed in the California Classic Brazilian jiu-jitsu tournament on November 15, 2009, in the black belt gi absolute division.
In a bout promoted as "catch wrestling vs. Gracie jiu-jitsu", Barnett secured a takedown in the opening minutes and maintained top position for the duration.
[71] On November 2, 2018, at the Catch Wrestling World Championships hosted by The Snake Pit in Bolton, England, Barnett competed and won the super heavyweight (100+ kg) division.
[75][76][77] Barnett competed against former KSW Heavyweight Champion Marcin Różalski in a bare-knuckle boxing match with elbows allowed on October 23, 2020, due to an agreement with Bellator.
[14] His grappling technique is based on catch, utilizing the controls, rides, and pinning holds to exert pressure over his opponent and grind him down when the fight gets to the ground.
[85] Barnett has also shown the ability to enhance his striking with catch wrestling, using collar ties and wrist grips to set up elbows and knees against the fence.
[91] It was inspired by a song by the British death metal band Bolt Thrower, itself named after a character from the sci-fi miniature wargame Warhammer 40,000.