Cullen O'Neil is a New York City-based cellist originally from Kalamazoo, MI. Performances have brought her across North America and Europe to venues such as Alice Tully Hall, the Kennedy Center, Mariinsky Hall in St. Petersburg, The Great Hall of the Moscow Conservatory, Royal Albert Hall as part of the BBC Proms, the Helsinki Musiikkitalo, and the Philharmonie de Paris alongside Les Arts Florissants. In 2021 she was inducted as a Fellow of The English Concert in America and in 2022 became a member of Boston Baroque. Cullen is also a founding member of Quartet Salonnières, a New York-based historical quartet, and Nuova Pratica, an ensemble of historically-inspired composer/performers.

Cullen graduated from The Juilliard School in 2021 with a master's degree in historical performance. Previously, she earned degrees in both cello and music theory from the University of Michigan, where she studied with Richard Aaron. She spent the 2017-2018 school year at the Sibelius Academy in Helsinki studying with Raimo Sariola.