Casey O’Neill

Casey O'Neill, known by the nickname "King," is a Scottish-born Australian competitor in the women's flyweight division of the UFC.

Born in Irvine, Scotland, O'Neill moved with her family to Australia's Gold Coast as a child. Her father, Cam O'Neill, a former kickboxer, introduced her to combat sports, and she began training in kickboxing before moving into mixed martial arts as a teenager. She developed on the Australian regional scene, most notably with Eternal MMA, where she won and successfully defended the promotion's women's strawweight championship. During her formative years she also spent time training at Tiger Muay Thai in Phuket, Thailand, crossing paths with the Shevchenko sisters.

O'Neill holds a brown belt in Brazilian Jiu-Jitsu, earned under coach Casey Halstead at 10th Planet Jiu-Jitsu, and trains out of Xtreme Couture in Las Vegas under head coach Eric Nicksick. That dual grounding in striking and grappling defines her approach inside the cage: a pressure-forward, high-pace style built on crisp boxing and kickboxing combinations paired with an opportunistic, finish-seeking ground game. She has described herself as a fighter who thrives in uncomfortable exchanges, applying constant forward pressure to break opponents down over the course of a fight.

Since making her promotional debut with the UFC in 2021, O'Neill has built a resume that includes a first-round submission finish of Lara Procopio and a hard-fought split-decision win over veteran contender Roxanne Modafferi, along with bouts against fellow flyweight standouts including Antonina Shevchenko.

Carrying a self-described "Scaussie" identity shaped by two countries, O'Neill has become one of the more distinctive personalities in the women's flyweight division, representing both her Scottish roots and her Australian upbringing inside the Octagon.