The 32-year-old fighter and former porn actor, whose birth name is Jon Koppenhaver, was captured by U.S. marshals in a hotel room in Simi Valley, a suburb northwest of Los Angeles where he once lived.
He is being held without bond on a federal charge of being a fugitive from justice in the Ventura County jail while he awaits extradition to Nevada, the Los Angeles Times reports.
Officers say the fighter, who legally changed his name in 2008, is the primary suspect in a dispute that left his ex-girlfriend, adult film actress Christy Mack, and her friend with serious injuries.
According to a statement Mack posted on Twitter on Monday, War Machine showed up unannounced at her house Aug. 8, found her and her friend unarmed, and beat her friend without uttering a word.
Mack said War Machine sent away the friend and turned to her, forcing her to shower before knocking out some of her teeth and breaking bones in her face. She wrote that she feared for her life as he sawed off her hair with a dull knife.
She said War Machine had been abusive in the past and broke up with her in May.
Court records filed Monday say the 32-year-old was wanted on suspicion of domestic battery, strangulation, lewdness, assault and coercion in the attack early Friday. Police issued the warrant Tuesday following its investigation.
Bellator MMA President Scott Coker announced last Friday his promotional company was dissolving its contract with the fighter in light of the accusations.
War Machine, who appeared on the reality show "The Ultimate Fighter," lost his only pay-per-view bout in 2008 and moved on to fight for a variety of MMA promotions over the past five years. He fought three times for Bellator last year, losing his final bout in October 2013.
The welterweight fighter has had previous run-ins with the law and missed two years of his career while he spent time in jail. His record includes a 2012 conviction for attempt to commit battery with substantial bodily harm.
U.S. marshals said they worked with police and Department of Homeland Security agents to capture Koppenhaver.
"This is yet another example of how our joint agency efforts are apprehending fugitives who think they can hide," District of Nevada U.S. Marshal Christopher Hoye said in a statement.
ESPN.com's Brett Okamoto and The Associated Press contributed to this report.
Fugitive War Machine Captured By Marshals
MMA fighter War Machine was captured by U.S. marshals on Friday on suspicion of beating his ex-girlfriend.