In 1973, Down was cast as Georgina Worsley, Marchioness of Stockbridge, on the Emmy Award-winning British drama series, Upstairs, Downstairs. This role was her career breakthrough, and after the show ended in 1975 she moved to Hollywood and began her film career. She starred in the 1976 movie The Pink Panther Strikes Again, and later was cast opposite Elizabeth Taylor on the film adaptation of A Little Night Music. Down worked as leading lady in film, and starred opposite Kirk Douglas, Laurence Olivier, Sean Connery, Anthony Hopkins and Donald Sutherland in various films. Her major roles were in The Betsy (1978), The First Great Train Robbery (1979), Hanover Street (1979), Rough Cut (1980), and her box-office bomb Sphinx (1981).