Born in London, England, Ella Purnell was cast in a London West End theatrical production of the musical Oliver at the age of 12. As a teenager, she appeared in Never Let Me Go (2010) and Kick Ass 2 (2013). Tim Burton cast her in Miss Peregrine's Home for Peculiar Children in (2016) and she starred alongside Brian Cox in Churchill a year later.
In 2020, Purnell starred in Belgravia, a period drama TV series from the creator of Downton Abbey. She then starred in her biggest feature to date when she appeared in the zombie action film Army of the Dead (2021), and she reprised her role in the sequel, Army of the Dead: Lost Vegas.