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).

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.

In addition to her work in film and theatre, Keller has developed a career in classical music as a speaker and opera director.

She has performed the speaking role of Joan of Arc in Arthur Honegger's oratorio Jeanne d'Arc au bûcher on several occasions, with conductors such as Seiji Ozawa[7][8] and Kurt Masur.

[12] The Swiss composer Michael Jarrell wrote the melodrama Cassandre, after Christa Wolf's novel, for Keller, who performed in the world premiere in 1994.