Casey O’Neill Bio
Casey O’Neill (born 7 October 1997) is a Scottish and Australian professional mixed martial artist who competes in the women’s Flyweight division of the Ultimate Fighting Championship (UFC). Known by the ring name “King,” she has built a reputation as an aggressive striker whose foundation was forged through years of kickboxing training. As of late March 2026, she is ranked among the top contenders in her division.
Standing 5 feet 6 inches tall with a 69-inch reach, O’Neill fights out of Las Vegas, Nevada, where she currently trains with Fight Ready. With a professional record built on knockouts, submissions, and durable decision wins, she represents one of the more compelling international stories in contemporary mixed martial arts.
Early Life and Background
Casey O’Neill was born in Irvine, Scotland, and spent the earliest years of her childhood in nearby Kilmarnock. Her father, Cam, was a professional kickboxer, and that family background introduced her to combat sports at a very young age. O’Neill began training in kickboxing herself at the age of four, laying the groundwork for the aggressive striking style that would later define her professional career.
At the age of 10, O’Neill moved with her family to Australia’s Gold Coast, where she attended Coombabah State High School. The relocation expanded her athletic horizons, and at 13 she began cross-training in other martial arts, including Brazilian jiu-jitsu. O’Neill ultimately earned a brown belt in Brazilian jiu-jitsu under Casey Halstead, demonstrating a well-rounded grappling base to complement her striking arsenal.
Path to MMA
Her father eventually allowed O’Neill to compete in her first amateur MMA fight at 15, where she was stopped in the first round by an opponent four years her senior. A second amateur bout the following year ended in another early first-round loss, prompting a deliberate two-year period of focused training. She returned to the amateur ranks at 19 and strung together five consecutive victories before turning professional at 21.
In 2019, O’Neill relocated to Phuket, Thailand, to train at the renowned Tiger Muay Thai gym, sharpening her striking under one of the most respected camps in the sport. That international experience helped her transition from the regional Australian scene to the global stage, setting the foundation for her signing with a major promotion.
Casey O’Neill Career
Early Career (2019–2020)
Casey O’Neill made her professional debut on 5 April 2019 at Eternal MMA 43, defeating Amira Hafizović by unanimous decision. She quickly piled up domestic wins against Jada Ketley, Miki Motono, and Caitlin McEwen, competing initially at strawweight before moving up to flyweight in 2020. One of those early bouts ended with a missed weight cut that forced her to vacate a title, an early lesson in the demands of professional fight preparation.
In September 2020, O’Neill accepted her first fight overseas with the UAE Warriors promotion and defeated Christina Stelliou via second-round knockout at UAE Warriors 13. Following that performance, she wrapped up her time at Tiger Muay Thai and transitioned to Xtreme Couture MMA in Las Vegas, where she would develop her game for the next several years.
UFC Breakthrough (2021–2022)
O’Neill announced herself on the UFC stage with a second-round knockout of Shana Dobson at UFC Fight Night 185 on 20 February 2021. She followed that debut with a third-round rear-naked choke of Lara Procópio at UFC on ESPN 25, showcasing her developing submission game. A technical knockout victory over Antonina Shevchenko at UFC Fight Night 193 in October 2021 earned her the Performance of the Night award and cemented her status as a prospect to watch.
In February 2022, O’Neill took a split-decision win over veteran Roxanne Modafferi at UFC 271, a result that 19 out of 19 media outlets scored in her favor. A scheduled bout with Jessica Eye at UFC 276 was derailed in late April 2022 when O’Neill tore her ACL, forcing her to withdraw and be replaced by Maycee Barber.
Setbacks and Return (2023–2024)
O’Neill’s return campaign hit early resistance. She dropped a unanimous decision to Jennifer Maia at UFC 286 in March 2023, and a planned booking with Viviane Araújo at UFC 293 fell through in early August when another injury forced her off the card. Closing the year at UFC 296 in December 2023, she was submitted by Ariane Lipski via second-round armbar, a second straight loss that tested her resolve.
After the difficult stretch, O’Neill made a team change, departing Xtreme Couture MMA in 2024 to join Fight Ready. She rebounded at UFC 305 in August 2024, when original opponent Tereza Bledá withdrew and Luana Santos stepped in; O’Neill took the fight and won by unanimous decision, signaling a return to form.
Fight Ready Era (2024–Present)
Settled into her new training environment, O’Neill continued to build momentum in the flyweight division. Her technical skill set expanded under the Fight Ready coaching staff, and she entered 2026 with renewed confidence and a clearer strategic approach. The team change appears to have reinvigorated her career trajectory after back-to-back injuries and losses.
Style and Strengths
O’Neill’s style is rooted in kickboxing, an inheritance from her earliest training under her father and later refined at Tiger Muay Thai. She combines sharp, technical striking with a growing submission game anchored by her Brazilian jiu-jitsu brown belt. Her finishing instincts and willingness to engage have produced a highlight reel built largely on knockouts and rear-naked chokes.
Notable Events and Milestones
Among her signature moments are her UFC debut knockout of Shana Dobson, her Performance of the Night-winning stoppage of Antonina Shevchenko, and her dominant decision win over Roxanne Modafferi. On 28 March 2026, she added a first-round technical knockout of Gabriella Fernandes at UFC Fight Night 271, further demonstrating her finishing ability at the top level.
Casey O’Neill Career Wins
Casey O’Neill’s verified professional record reflects a finisher-first approach, with the majority of her victories coming inside the distance. Across her regional and UFC appearances, she has consistently delivered decisive results against a mix of rising prospects and established veterans.
UFC Highlights
Inside the UFC, O’Neill has secured multiple finishes, including her debut knockout of Shana Dobson, the rear-naked choke of Lara Procópio, and her technical knockout of Antonina Shevchenko that earned Performance of the Night honors. Her unanimous decision over Luana Santos at UFC 305 and her first-round technical knockout of Gabriella Fernandes at UFC Fight Night 271 bookend a run of form that has her climbing back toward title contention.
Other Wins and Performances
Outside the UFC, O’Neill captured regional victories on the Australian circuit and added a second-round knockout of Christina Stelliou at UAE Warriors 13. Her amateur career featured a five-fight winning streak that persuaded her to turn professional in 2019.
Casey O’Neill Family
Family Background and Fighting Lineage
Casey O’Neill’s entry into combat sports was shaped by her father, Cam, a professional kickboxer who introduced her to training at the age of four. That direct family lineage gave her an early technical foundation and a deep familiarity with fight preparation uncommon for someone her age.
Personal Life
O’Neill relocated from Scotland to Australia’s Gold Coast as a child and later settled in Las Vegas, Nevada, where she currently resides and trains. She has kept much of her personal life private, and no public information regarding a spouse or children has been confirmed.
2025 Season Performance
Heading into 2025, Casey O’Neill was working to reestablish herself in the UFC women’s flyweight rankings after injuries had interrupted her momentum. Her unanimous decision win over Luana Santos at UFC 305 in August 2024 served as the foundation for the year, demonstrating improved conditioning and a more measured approach inside the Fight Ready system.
Throughout 2025, O’Neill focused on consistency and durability, two areas that had been tested by her earlier ACL tear and subsequent setbacks. While specific bout outcomes during the calendar year are not fully documented in available sources, her training camp stability and ranking trajectory suggested a return to form.
Looking ahead, O’Neill entered 2026 with clear momentum, capping a strong run of preparation with a first-round technical knockout of Gabriella Fernandes at UFC Fight Night 271 on 28 March 2026. With her ranking on the rise and a settled team behind her, she remains a compelling contender to watch in the women’s flyweight division.