Keller's earliest film appearances were in "Funeral in Berlin" (1966, in which she was not credited) and the German film "Wilder Reiter GmbH" (1967). She appeared in a series of French films in the 1970s, including "Un Cave" (1971), "La Raison du Plus Fou" (1973) and "Toute Une Vie/And Now My Love" (1974). Her most famous American film appearances are her Golden Globe-nominated performance as Dustin Hoffman's girlfriend in "Marathon Man" (1976) and her performance as a "femme fatale" Palestinian terrorist who leads an attack on the Super Bowl in "Black Sunday" (1977). Keller acted alongside Al Pacino in the 1977 romantic drama film "Bobby Deerfield", based on Erich Maria Remarque's novel "Heaven Has No Favorites", and subsequently the two were involved in a relationship. She also acted alongside William Holden in Billy Wilder's 1978 romantic drama "Fedora."