American motion picture screenwriter whose 25-year career spanned the silent and sound eras.

As a young adult, Marion had twice married and divorced and had tried her hand as a journalist, model, and illustrator before going to Hollywood in 1913. She worked with director Lois Weber in 1914 and experimented with different aspects of film work, but she discovered her true calling in 1915 as a scriptwriter. After a hiatus as a war correspondent in France (1918–19), she returned to work as a scriptwriter and also directed a few films, including two starring her third husband, Fred Thomson. During the 1920s she drafted many a successful script for such stars as Mary Pickford (Pickford, Mary), Marion Davies, Ronald Colman (Colman, Ronald), and Rudolph Valentino (Valentino, Rudolph) and was among the highest-paid screenwriters in the business.

Marion's first sound script was for Anna Christie (1930), an adaptation of Eugene O'Neill (O'Neill, Eugene)'s play that was also Greta Garbo (Garbo, Greta)'s sound debut. Marion successfully lobbied to have her friend Marie Dressler (Dressler, Marie) cast in a supporting role in the film and further helped to revive Dressler's career by scripting Min and Bill (1930) for her. Dressler won an Academy Award for that film, which costarred Wallace Beery (Beery, Wallace). Marion wrote several other screenplays for Beery, including The Big House (1930) and The Champ (1931), both of which won her Academy Awards. In 1940, after writing more than 130 screenplays, Marion retired but continued writing novels and stories. For a time, she also taught scriptwriting at the University of Southern California. Her memoirs of her Hollywood years, Off with Their Heads, appeared in 1972.

Marion is recognized as one of Hollywood's most significant film writers. She was acclaimed for her skill at writing scenarios and adaptations that highlighted a star's particular talents, her ability to create original, genuine characters, and her sometimes spare use of dialogue. Her early experience during the silent era taught her to make use of the visual strengths of film and of the facial expressions of actors to convey meaning. Included among her notable films are Poor Little Rich Girl (1917), The Son of the Sheik (1926), Dinner at Eight (1933), and Camille (1937).