O'Neil started his professional MMA career in 2006 at the age of 21. He lost his inaugural fight to Earl Bauer via an inverted triangle choke submission. Since then, O'Neil has fine tuned his skills while training with the likes of John Howard, Rick Hawn, Joe Lauzon and Tom Lawlor. In 2008, O'Neil captured the Reality Fighting welterweight championship. He lost this title in 2009 to Tim Pinney via a heel hook. O'Neil went on to win his next 3 bouts while also winning the Cage Titans FC welterweight title.
''The Ultimate Fighter''
O'Neil signed with the UFC in 2011 to compete on. O'Neil was selected as an alternate for the T.V. show and received his chance to compete once Myles Jury of Team Lesnar was forced to withdraw due to injury. In Chuck's first bout of the competition he fought Zach Davis and lost via a triangle choke in the first round. Luckily, Dana White chose Chuck to occupy one of the two "wild card" positions; keeping him in the running for the grand prize of a six figure UFC contract. O'Neil faced Team dos Santos' Javier Torres in the "wild card" bout. Chuck was able to defeat Torres via a D'Arce choke in the second round of the fight. The win moved him into the quarter-finals. O'Neil then had a rematch with Zach Davis in the quarter-finals. O'Neil was able to dominate Davis this time around and win by unanimous decision after two rounds. O'Neil then moved into the semi-finals and fought teammate, Tony Ferguson. O'Neil was eliminated from the competition after losing to Ferguson via a third round stoppage.
Ultimate Fighting Championship
Even though O'Neil lost in the TUF 13 semifinals, he remained signed with the UFC after the show. He made his official UFC debut June 4, 2011 on The Ultimate Fighter 13 Finale card, fighting against fellow semifinalist and teammate, Chris Cope. He lost the fight via unanimous decision, and subsequently was released from his contract on June 17, 2011.
Post UFC
O'Neil fought fellow former UFC fighter Marcus Davis in a main event bout at W-1 Reloaded on October 15, 2011. He won the fight via split decision. O'Neil next faced Kevin Nowaczyk at Hoosier Fight Club 11 on June 2, 2012. He lost the fight via unanimous decision. Yet, O'Neil rebounded strong in his next bout by earning a unanimous decision victory vs Keith Jeffrey at "CES MMA: Battle Tested". O'Neil next faced Ralph Johnson at "CES MMA: New Blood". O'Neil scored a TKO victory over Johnson in the first round. O'Neil next faced Gil de Freitas at "CES MMA: Gold Rush" in Lincoln, Rhode Island and suffered his first career TKO defeat. O'Neil returned to form in his next bout by getting his own TKO victory over the well traveled MMA veteran Chris "Cappi" Woodall at "CES MMA: November to Remember". Chuck O'Neil remained in the winners circle as he earned a unanimous decision victory over Roger "The Leprechaun" Carroll at "CES MMA 22". Chuck O'Neil next faced Ricardo Funch at "CES MMA 26" on October 10, 2014 for the vacant CES MMA Welterweight Title. O'Neil slapped on a second round armbar, submitting the UFC vet and securing the welterweight championship belt. On January 30, 2015, Chuck O'Neil continued his winning ways with a 1st round knockout victory over Emmanuel Walo at "CES MMA 27" to retain the welterweight belt. Chuck O'Neil next faced Dominique Steele at "CES MMA 29" to defend the Classic Entertainment and Sports Welterweight Belt. He lost via unanimous decision in a five round war. Chuck O'Neil moved to the middleweight division for his next bout versus Daniel Vizcaya at "CES MMA 31" and suffered his first submission loss since 2009 as Vizcaya executed a 1st round rear-naked choke. Following the Vizcaya fight, O'Neil stayed active in the middleweight division and won his next two fights versus Dennis Olson and Roy Jones.
