In his interview with François Truffaut, Alfred Hitchcock said he was so impressed with the performance of Anita Björk in Miss Julie (1951) that he hired her for this movie. However, when she arrived in Hollywood, Bjork brought her lover, writer Stig Dagerman, and their baby daughter. Since they were not married, Warner Bros. insisted that Hitchcock find another actress for the role of Ruth Grandfort, in this case Anne Baxter.
Montgomery Clift drank during the shooting and his eyes appear glazed during the ferry scene. Alfred Hitchcock was a very non-confrontational director and delegated an assistant director and Karl Malden to talk to the actor about it.
Alfred Hitchcock, as was his custom, created detailed storyboards for each scene. He could not understand Montgomery Clift's Method acting technique and quickly became frustrated with Clift when he blew take after take for failing to follow Hitchcock's instructions.
The film had one of the longest "preproductions" of any Alfred Hitchcock film, with almost 12 writers working on the script for Hitchcock over an eight-year period. (Hitchcock had taken time off for the wedding of his daughter Patricia Hitchcock in 1951, and Hitchcock was in the midst of dissolving his partnership in Transatlantic Pictures with Sidney Bernstein.)
Cognizant of the difficulty non-Catholics would have in understanding the priest's reluctance to expose Keller, Alfred Hitchcock said, "We Catholics know that a priest cannot disclose the secret of the confessional, but the Protestants, the atheists, and the agnostics all say, 'Ridiculous! No man would remain silent and sacrifice his life for such a thing.'"
Alfred Hitchcock, who was reared a Catholic, had expressed interest in filming the story as early as the 1930s. In 1948, according to a modern source, Hitchcock and his wife Alma Hitchock wrote a treatment of the play, and a May 1948 Hollywood Citizen-News news item announced that Van Johnson would play the part of the priest. Thereafter, at least three other writers, William Rose, Leslie Storms and Paul Vincent, worked on drafts of the script, and Hitchcock and his wife Alma tried unsuccessfully to interest both Graham Greene and Samson Raphaelson in the project.