Sonnen is often considered one of the best mixed martial artists never to have won a major MMA world championship and one of the sport's greatest trash-talkers.

[21] Sonnen started his mixed martial arts career in 1997 at the age of 19, by defeating Ben Hailey in Vancouver, Washington.

In late 2003, he was submitted by future Ultimate Fighter winner and UFC Light Heavyweight Champion Forrest Griffin with a triangle choke submission maneuver.

He went on to win a unanimous decision over Alexey Oleinik, defeat Tim McKenzie in 13 seconds with a D'arce choke, and finish UFC and PRIDE veteran Amar Suloev via TKO.

Keith Kizer, executive director of the Nevada State Athletic Commission, claimed Sonnen only yelled "No" after the referee stopped the fight.

The principal grounds of his appeal were that he had a medical justification for taking testosterone, and he believed he had taken the necessary steps to disclose the condition and its treatment to the CSAC.

[45] He said he had previously disclosed his condition to the CSAC before his UFC 104 bout with Yushin Okami, which took place in Los Angeles on October 24, 2009.

[46] Based on his testimony, the CSAC voted to recharacterize Sonnen's transgression as a failure to properly disclose a medical treatment, and correspondingly reduced his suspension from twelve months to six, ending March 2, 2011.

However, in the third week of April 2011, the CSAC announced it had reversed its decision to lower his sentence, and had placed him on indefinite administrative suspension due to his conviction for money laundering (see below) and his possibly false testimony during the hearing of December 2, 2010.

After hearing testimony from Keith Kizer via streaming video, as well as from Sonnen and his supporters, the CSAC voted 4–1 to uphold the suspension.

Two days later, the CSAC clarified that the applicable regulations only allowed Sonnen to be suspended until his existing license expired (on June 29, 2011).

[67] But the rematch with Griffin was scrapped after Sonnen was named as a coach for The Ultimate Fighter 17 against Light Heavyweight Champion Jon Jones.

[69] Some fighters were upset with his title opportunity because Sonnen, "arguably the most legendary talker in UFC history",[70] had not fought since returning to the light heavyweight division.

[71][72][73] Dana White defended the matchup, saying "Sonnen was willing to fly over to Las Vegas to fight Jones on the same day", while other contenders like Maurício Rua and Lyoto Machida turned the offer down.

[74][75] Jon Jones showed a lack of interest in the fight and downplayed the contest, making it clear that he did not believe Sonnen to be a worthy contender.

In an interview, Sonnen did his best to hype up interest but Jones gave him "silent treatment", refusing to make eye contact.

[76] Jones dispatched the challenger using Sonnen's own style of dominant top control and ground and pound to defeat him via TKO in the first round.

[78][79][80] Sonnen was expected to face Maurício Rua on June 15, 2013, at UFC 161, replacing Antônio Rogério Nogueira, who had pulled out of the bout citing a back injury.

[81] However, issues relating to obtaining a visa meant Sonnen was not able to get into Canada, and Rua ended up being pulled from the event altogether.

[88] Dana White later stated the fight had to be rescheduled because Silva injured his hand from a brawl with Sonnen that took place during the filming of the show.

[92] Following the controversy of his second failed drug test, Sonnen announced on the June 11, 2014, episode of UFC Tonight his retirement from MMA competition.

[95] On July 23, 2014, the NSAC ruled that Sonnen would be suspended for 2 years from martial arts competition worldwide due to his multiple failed drugs tests.

[114] The promotion ran several live events and tapings for a potential television show, which would end up being called GFW Amped.

Sonnen joined the GFW Amped broadcast team as an "expert analyst", making his return to professional wrestling after nearly 17 years.

[115] GFW Amped ultimately did not get picked up by a television network but did later air as part of Impact Wrestling's One Night Only pay-per-view series.

[14] On September 2, 2015, it was announced that Sonnen signed with the World Series of Fighting to become a member of their broadcast team beginning at WSOF 23.

[118] Sonnen faced Anderson Silva on June 15, 2024 in a five-round, two minute exhibition boxing bout at 216 pounds in São Paulo, Brazil.

[168] Gamble filed a counter lawsuit seeking $400,000 in damages from Sonnen for defamation, wage reimbursement, and his ownership interest in the business.

When the door opened, Sonnen allegedly got into a physical altercation with multiple people, prompting hotel guests to call 911.

He was fired by host Arnold Schwarzenegger in the show's 4th week after it emerged that Sonnen had deliberately cut his team's computer cord in order to gain them more time.