Popplewell, eldest of three children, is the daughter of Andrew Popplewell and Dr. Debra Lomas. She has two younger siblings, Lulu Popplewell, who is also an actress and starred in Love Actually alongside Popplewell's Narnia co-star Liam Neeson, and Freddie Popplewell who starred as Michael Darling in the movie Peter Pan. She attended North London Collegiate School and was Head Girl 2006-2007. Since 2007, Popplewell has been a student of English at Magdalen Collage, Oxford. Popplewell currently resides in Highbury, North London.