[2][3][4] O'Neill was born in Japan to a Japanese mother, Sumie, and a New Zealand father, Chris, a professional rugby player.

[5] In 2009, O'Neill won the Prix de Lausanne, the world’s most prestigious competition for young dancers.

[8] The next year, she won first place in the senior woman's section at the Youth America Grand Prix in New York.

In 2020, O'Neill danced The Swan in Misty Copeland's fundraiser, Swans for Relief, a response to the impact of the COVID-19 coronavirus pandemic on the dance community, with funds going to participating dancers' companies and other related relief funds.

[8] In 2016, she received the Best Female Dancer award at the Benois de la Danse competition for her performance in the title role of the ballet Paquita.