Watson was born in Paris, France, the daughter of English lawyers Jacqueline Luesby and Chris Watson. Watson lived in Maisons-Laffitte near Paris until she was five. Her parents divorced when she was young, and Watson moved to England to live with her mother in Oxfordshire while spending weekends at her father's house in London. Watson has said she speaks some French, though "not as well" as she used to. After moving to Oxford with her mother and brother, she attended the Dragon School, remaining there until 2003. From age six, she wanted to become an actress, and trained at the Oxford branch of Stagecoach Theatre Arts, a part-time theatre school where she studied singing, dancing, and acting.