[3] She also attended weekly classes at the Sylvia Young Theatre School, studying acting, singing, and dance, and was represented by their in-house talent agency.

Finishing her A-Levels in Philosophy, English, Drama and Music,[4] at the age of 18, Purnell intended to put a pause on her acting career, and earn a place at university with the intention of becoming a children's writer or teacher.

She described her decision to defer university as "bittersweet at first because it felt like a lost opportunity of a different path in life" but was glad she chose acting.

[7] Towards the end of her time in the show, she was cast as the younger version of Keira Knightley's character in Mark Romanek's film Never Let Me Go (2010).

She then took a break from acting, but returned to star in Tim Burton's film Miss Peregrine's Home for Peculiar Children (2016) as she had always wanted to work with him.

[14] Purnell appeared as Hester Argyll in the BBC miniseries Ordeal by Innocence (2018)[15] and starred as Tess in the Starz series Sweetbitter (2018).