Trivia

Director Cameo: [Alfred Hitchcock] Five minutes into the film, in the hotel corridor as Marnie walks by.

Diane Baker was not allowed to read the script of the film before choosing whether or not to do it. She was only told that it was an Alfred Hitchcock movie named Marnie starring Tippi Hedren.

Diane Baker has said that for the scene where she eavesdrops on Mark and Marnie talking outside of the house, Alfred Hitchcock came up to her, put his hands on her face, and physically manipulated it into having the expression he wanted for the scene.

Alfred Hitchcock first asked Evan Hunter, the screenwriter for The Birds (1963), to adapt the novel after Tippi Hedren had signed on. However, Hunter strongly objected to the scene in the novel where Mark rapes Marnie, as he felt it was "unheroic" and that it would make women in the audience hate Mark. When he pressed Hitchcock about changing the scene, Hitchcock fired him. Jay Presson Allen, who took over as screenwriter, stated that opposition to the rape scene doomed Hunter since that scene was the main reason Hitchcock wanted to do the film. For her part, Allen said she never had any qualms about including the scene, and felt it was up to Sean Connery and his charisma to make the audience "forgive" Mark's actions.

Joseph Stefano originally wrote a screen adaptation of the novel when Grace Kelly was supposed to star. Stefano's adaptation was much truer to the original book, and would have included two important characters from the novel that never made it into the final version of the film. One was a psychotherapist that Marnie was seeing at Mark's insistence, whose role ended up being merged into Mark's. The other was a man named Terry who was a co-worker of Mark's and also in love with Marnie. The part of Terry was massively reworked and ended up becoming Lil.

Screenwriter Jay Presson Allen thought that the expensive car Mark drove and the fancy clothes worn by his father were ridiculous and out of place, but Alfred Hitchcock insisted that they were necessary to convey the proper feeling of Mark being part of an "American aristocracy" to the audience.

Alfred Hitchcock was loathe to use a mechanical horse to film the shots of Marnie riding, but sent a crew member to inspect a mechanical horse owned by Disney that was supposed to be the best in existence. Walt Disney spotted the crew member on the Disney lot and personally offered to let Hitchcock use it, which he did.

Alfred Hitchcock wanted Grace Kelly to make her screen comeback in the title role, but the people of Monaco were not happy with the idea of their princess playing a compulsive thief.