Known for her collaborations with directors Elia Kazan, Sidney Lumet and Frank Perry, she received two Academy Award nominations for her work on The Godfather (1972) and Ragtime (1981).

Johnstone's credits include East of Eden (1955), Baby Doll (1956), David and Lisa (1962), The Group (1966), The Godfather (1972), The Taking of Pelham One Two Three (1974), The Stepford Wives (1975), Dog Day Afternoon (1975), and Running on Empty (1988).

[1] Johnstone got her start working on student productions at Barnard College, later becoming a seamstress for summer stock stage shows.

Her other stage productions included Bell, Book and Candle, Tea and Sympathy, and A Streetcar Named Desire.

In 1948, Johnstone made the move to working in films, obtaining her first costume design credit on Portrait of Jennie.