Facing the twilight of his amateur wrestling career, Coleman transitioned to the then-new sport of mixed martial arts after accidentally turning on a TV channel where the
UFC 1 was ongoing. In what turned out to be a long battle, Coleman lost a decision after 21:00 (regulation plus two overtimes). This was considered to be one of the largest upsets in UFC history at that time, largely because of the way Coleman had dominated his opponents in his previous fights. Coleman took nearly a year off after having to get
ACL surgery and returned at
UFC 17. Coleman was originally scheduled to face
Randy Couture in a title match for the UFC Heavyweight Championship, but Couture was injured during training and was forced to pull out of the fight. Coleman instead faced a relatively unknown (at that time) last-minute replacement fighter, up and coming
Lion's Den product
Pete Williams. In what turned out to be another long and strenuous battle, Coleman appeared to be completely exhausted after 10 minutes; he was fatigued to the point of resting his hands on his knees during the fight. Williams took advantage of Coleman's fatigue and landed a heavy kick to the face, knocking 'The Hammer' out for the first time in his career. After his loss to Pete Williams, Coleman went to train with former UFC champion
Ken Shamrock and his
Lion's Den training camp for his upcoming bout with feared Brazilian striker
Pedro Rizzo at
UFC 18. The fight with Rizzo was part of the "Road to the Heavyweight Title", which was a four-man tournament between Coleman, Rizzo,
Bas Rutten and
Tsuyoshi Kosaka that would crown the next UFC Heavyweight Champion. After 15:00 the fight went to the judges, and they awarded a split decision win to Rizzo. The decision was controversial, with many and Coleman himself believing he did enough to win. In a 2010 interview, Coleman said he still feels the effects of the controversial decision loss to Rizzo. In response to questions about the fight's legitimacy, Coleman said, "It was what it was. I needed to support my family. They guaranteed me another fight after that and I needed that security. It was what it was. I'm going to leave it at that." Coleman won the
Pride 2000 Open Weight Grand Prix tournament defeating
Masaaki Satake,
Akira Shoji,
Kazuyuki Fujita, and
Igor Vovchanchyn. The final was scheduled to be fought with a 20-minute time limit but according to Coleman, the day before the fight the rules were changed to no time limit. The change forced him to modify his game plan to attempt a quick finish as he did not believe he could put Vovchanchyn away with his ground and pound in a long match. An outraged Chute Boxe refused to accept Coleman's backstage apology. The Chute Boxe team was assigned a yellow card for instigating this infraction. Coleman's contract was fought out at this point, and he subsequently re-signed with the organization. and lost via submission (armbar) at 1:17 of round two. Mark Coleman appeared with teammate,
Kevin Randleman, on the
US pay-per-view broadcast of the final
Pride event,
Pride 34: Kamikaze, stating that he intended to keep fighting.
Return to UFC (2008–2010) At
UFC 82, Mark Coleman was inducted into the
UFC Hall of Fame, making him the 5th inductee. Coleman announced that he was not retiring and would return to the octagon to fight
Brock Lesnar on August 9 in
Minneapolis at UFC 87. However, Coleman injured his knee while training, and was forced to pull out of the event.
Heath Herring replaced Coleman for the fight. Coleman faced
Maurício Rua in a rematch in their first bout in the UFC at
UFC 93 and lost by technical knockout as a result of punches late in the third round. This fight earned him a $40,000
Fight of the Night award.
Retirement from MMA After going over three years without competing Coleman announced via
Facebook that he has officially retired from MMA competition at 48 years of age.
UFC 300 After Coleman saved his parents from a burning house in March 2024, fighter
Max Holloway suggested that Coleman be the one to present the symbolic "BMF" ("baddest motherfucker") belt to the winner of the title fight at
UFC 300 on April 13, 2024. This request was granted and Coleman ended up wrapping the belt around Holloway, who was victorious in his bout against
Justin Gaethje.
Fight Circus On January 12, 2025, Coleman returned to the ring and competed at
Fight Circus 12 in
Phuket, Thailand in a "wheelchair boxing match" against the CEO of the promotion Jon Nutt. Both fighters were strapped into a wheelchair and were pushed around the ring by their cornermen with Coleman's cornerman being former UFC fighter
Matt Brown. At the end of the fight, both men stood up from their wheelchairs and Coleman knocked out Nutt at the last second. ==Professional wrestling career==