Olivia de Havilland wisely chose William Wyler as her director, considering that such a meticulous director would be able to coax a strong performance from her. As it turned out, Wyler became a staunch supporter of his leading actress, particularly in regard to the sneering attitude that Montgomery Clift displayed toward her (he didn't value her talents as an actress) and Ralph Richardson taking every opportunity to steal scenes from under her nose with his improvisations.
The song sung by Montgomery Clift while playing the piano is originally a vocal romance, "Plaisir d'amour", composed in 1784 by classical composer Jean-Paul-Égide Martini (August 31, 1741 - February 10, 1816), and was the basis for Elvis Presley's 1961 hit "I Can't Help Falling In Love With You" written for the movie Blue Hawaii (1961).
In his autobiography, Basil Rathbone lamented that he did not get the part of Dr Sloper in the film, following his performance in the play in New York, opposite Wendy Hiller. Had he been cast, and had Errol Flynn won the part of Morris Townsend as originally planned, this would have been a re-teaming of all three main stars from the film classics, "Captain Blood" (1935) and "The Adventures of Robin Hood" (1938.
During the spiral staircase scene, director Billy Wyler made thirty seven takes with Olivia De Havilland. Only after the last one, when she fell of exhaustion, Wyler declared that was the one he wanted to keep in the box.
After seeing The Heiress on Broadway, Olivia de Havilland approached William Wyler about directing her in a screen adaptation of the play. He agreed and encouraged Paramount Pictures executives to purchase the rights from the playwrights (Ruth and Augustus Goetz) for $250,000 and offer them $10,000 per week to write the screenplay. The couple were asked to make Morris less of a villain than he was in their play and the original novel in deference to the studio's desire to capitalize on Montgomery Clift's reputation as a romantic leading man.
In a letter to the New York Times, Aaron Copland denied having composed the music used for the opening credits. His composition for the credits was deemed too challenging for audiences and was replaced at the request of the producer.
Although the score is credited to Aaron Copland, William Wyler disliked it, and had it heavily rewritten and reorchestrated, possibly by Hugo Friedhofer who had orchestrated many of Max Steiner's and Korngold's lush operatic Warner Bros. scores, and Wyler's The Best Years of Our Lives (1946). What distinguished Copland from the usual Hollywood brand of orchestration was the simplicity and transparency of his scoring, and it was its spareness that so disturbed Wyler. The music sounds completely unlike any other piece of music Copland ever wrote, and it is no wonder he disowned it. Alex North, Copland's pupil, was more successful using this chamber music sound, notably in North's first film score A Streetcar Named Desire (1951). But Copland was ahead of his time.
The film was originally going to be produced by Liberty Films, Inc., an independent production company headed, in part, by William Wyler, but when Paramount absorbed the production company in 1948, the studio took on the film.
The trivia item below may give away important plot points.
To help Olivia de Havilland achieve the physically and emotionally weary and worn effect that he wanted, director William Wyler packed books into the suitcases that the actress lugged up the staircase in the scene where her character realizes that she has been jilted by her lover.