He was born in Chelsea, London, the brother of actor James Fox and film producer Robert Fox. The actress Emilia Fox is his daughter by his long-standing relationship with Joanna David.
Fox made his first film appearance in 1963, as an extra in This Sporting Life. In the late 1960s and early 1970s he began to establish himself with roles in classic British films such as The Go-Between and Battle of Britain. However, it was as the assassin in 1973's The Day of the Jackal that he made the biggest impression, and from then on he was much sought after. In 1980, he played King Edward VIII in the television drama series, Edward and Mrs Simpson.