Born in Teddington, the daughter of the American vaudeville performer and actor Fred Duprez, she began acting in her teens with a theatre company and made her first film The Crimson Circle in 1936. Her next film The Cardinal (1936) was also a success but it was her third film The Four Feathers that made her a star.

Her success continued with The Spy in Black (1939) and The Thief of Bagdad (1940) which she made for Alexander Korda. Korda took charge of her career after this point and took her to Hollywood where he set her asking price at $50,000 per movie. However, as Duprez had not yet achieved the level of popularity in America that she had in Britain, Korda's tactic only served to place her out of contention for most roles. She appeared in None But the Lonely Heart (1944) and The Brighton Strangler (1945) before playing what would arguably be her most successful role, in Rene Clair's film version of Agatha Christie's And Then There Were None. After a few more films, Duprez retired. Some sources state that she appeared uncredited in The Last Tycoon (1976) however her final credited performance was in One Plus One (1961).

Duprez lived in Rome, Italy for several years before returning to London where she died in her sleep after a long illness.