In 2017, she married Ollie Clueit, bassist of Meanwhile, Back in Communist Russia.... On graduating from Guildhall, O'Neil was awarded the 2009 Spotlight Showcase prize for Best Actress.
[5] O'Neil and her Match.com advert co-star, Steven Mitchell, also appear in the music video for 'She Began To Dance' sung by Matthew P. The music video shows the couple in similar but not identical outfits leaving the unidentified train station and going on a date to the beach.
[6] In 2014 O'Neil appeared in King Lear[7] alongside Frank Langella and in Richard III[8] with Martin Freeman, playing Regan and Lady Anne respectively.
In 2015 she appeared in a 2-part episode "Squaring the Circle" in Series 18 of BBC One's Silent Witness as young City DI Sarah Parks.
In 2023, she originated the role of Angie in the world premiere of James Graham's adaptation of Alan Bleasdale's Boys from the Blackstuff at Liverpool's Royal Court, and its subsequent transfer to the National Theatre and the West End in 2024.