He made his mixed martial arts debut at the age of 17, facing the 27-year-old Al "Superman" Dill in a Virginia Beach event.
During the event, a riot broke out, and Miller was punched in the back of the head by fellow fighter Mark Moreno.
On September 2, 2006, Miller won the Icon Sport Middleweight title from Robbie Lawler in a back and forth battle.
After being staggered and nearly finished by Lawler, Mayhem secured an arm triangle choke and won via submission in the third round.
In December of the same year, Mayhem lost his first title defense to Frank Trigg via TKO in the second round, a fight in which he was favored to win.
Miller stepped into the Dream 4 tournament on short notice, progressing to the semifinals before his eventual elimination by Ronaldo Souza in the quarterfinals.
After a period of verbal sparring on Japanese, Brazilian and American media, Miller and Souza fought a rematch for the Dream Middleweight belt, which had recently been vacated after Gegard Mousasi's departure to the Light Heavyweight division.
The fight ended in a no-contest after Miller landed an illegal soccer kick to Souza's forehead, opening a large gash and prompting a doctor's stoppage.
On April 17, 2010, Miller defeated Tim Stout at Strikeforce: Nashville by ground and pound TKO at 1:47 of the first round.
Miller was expected to face Robbie Lawler on June 16, 2010, at Strikeforce: Los Angeles, but was removed from the card after the Tennessee Athletic Commission suspended him for his part in the Nashville Brawl.
On April 22, 2011, Miller announced via Twitter that in the wake of his Strikeforce contract expiration, he had signed a multi-fight deal with the UFC.
The fight was eventually broken up by referees, members of Dan Henderson's corner and the promoter's security personnel.
[16] On October 8, 2012, Miller appeared on Ariel Helwani's internet talk show the MMA Hour to promote his upcoming film Here Comes the Boom.
[22] In a 2016 interview with Chael Sonnen, Miller said that the loss to Schiavolin helped him to begin to turn his life around from the legal troubles and drug addiction that have plagued him since his retirement in 2012.
[23] Miller competed in the Southern California Pro-Am Invitational 2003, beating Kenny Bond and Sean Spangler to make it to the semi-final, where he lost to Rener Gracie.
The charge was dismissed when the pastor, the complaining witness in the case, thought it would be best to give Miller spiritual guidance as opposed to jail time.
[30] On October 9, 2013, Miller was taken into custody for a misdemeanor contempt of court charge for violating a no-contact restraining order by sending a Snapchat message to the alleged victim.
[31] Miller was arrested on a felony domestic violence warrant on October 9, 2014, after a five-hour-long standoff with a SWAT team outside his Orange County, California, home.
Video footage from a bystander showed a handcuffed Miller outside the bar, shouting expletives and fighting with police officers.
[36] On July 11, 2016, Miller was arrested in Costa Mesa, California, and charged with two counts of assault and battery after allegedly injuring a security guard and spitting on a police officer at the Saddle Ranch Chop House restaurant.
[38] On October 23, 2018, Miller was arrested on charges of felony vandalism in Orange County after destroying property at his girlfriend's La Habra, California, home.
The felony vandalism charge carried a maximum penalty of eight months in jail, but due to the nature of the incident, prior convictions, and a probation violation, Miller faced up to 23 years in a California state prison.
[39][40] While he initially pleaded not guilty, on July 19, 2019, it was reported that Miller had accepted a plea deal and was sentenced to one year in jail with time served being credited.
Miller was transported to the Los Angeles County Men's Jail, where he was booked on charges of felony domestic battery and resisting arrest.
While the complaining witness initially did not take legal action, the man was hospitalized after the incident, discovered his ribs had been broken, and later chose to press charges.
He also appears in video games: Electronic Arts' EA Sports MMA and THQ's UFC Undisputed 3.
Miller also appears in Here Comes the Boom, in which he plays the role of "Lucky" Patrick Murray, an MMA fighter who goes in the ring against Kevin James's character, Scott Voss, in the film.