Ellis was born in Chatham, Kent, England. Her father was a soldier, stationed during her childhood at various places in England and Germany. Accordingly, she attended seven schools in the two countries, including Russell House School between the ages of five and seven, and St Hilary's between the ages of 11 and 13 (both in Sevenoaks, Kent), and from the ages of 13 to 17 her last school was Richmond County School for Girls in Surrey. Having expressed an interest in acting since the age of five, she applied to and was accepted by the Central School of Speech and Drama in London, but was asked to defer her entry for a year as she was considered to be too young. She spent the year gaining experience of the acting world by working backstage at the Comedy Theatre in central London and as an assi