Composer Stephen Sondheim, notoriously protective of his stage works, long resisted offers to film this story. When Tim Burton expressed interest, however, Sondheim relented when pleased with Burton's vision for the project, and on the condition that the composer would maintain casting approval. Burton would only agree to direct with Johnny Depp in the lead, and though Sondheim feared Depp's vocals would be too "rock oriented," the composer approved the actor after a vocal audition. To approve the casting of Helena Bonham Carter, and to combat any rumor of nepotism (as Carter and Burton were romantically involved), the actress sent Sondheim no less than twelve audition tapes of her singing. Very impressed with her vocals, Sondheim immediately approved the actress. Also, in his 2010 book about his career as a songwriter, "Finishing the Hat," Sondheim states this is the only adaptation of one of his works for the screen for which he approves.
Helena Bonham Carter rehearsed her songs while practicing baking techniques, in order to perfect the quick, syncopated rhythm of the music.
In some of the scenes where Sweeney opens his razor very quickly, it is a mechanical razor. There is a button Johnny Depp would press to have the razor open, which he hides with his finger. Depp personally requested the prop department design this razor for him, as he had difficulty handling the real razors.
For his audition, Sacha Baron Cohen sang the entire score of Un violon sur le toit (1971) for director Tim Burton.
Tim Burton insisted that the film be bloody, as he felt stage versions of the play, which cut back on the bloodshed, robbed it of its power. For him, "Everything is so internal with Sweeney, that the blood is like his emotional release. It's more about catharsis than it is a literal thing."