The movie begins with a man named Sweeney Todd going to London with a help from a sailor, Anthony Hope. While sailing, Todd reveals that he is once used to be a barber who has everything, but the corrupt Judge Turpin took his wife, Lucy, away from him.
Inside her store, Mrs. Lovett serves Todd with pie. Then, she reveals about Benjamin Barker's wife that she is raped by Turpin when she is forced to go to his party. Todd screams about it, leading Lovett to realize that he is Barker. When Todd asks where his wife and daughter, Johanna are, Lovett replies that his wife took poison while his daughter is raised by Turpin to be his ward. Angered, Todd swears revenge.
Meanwhile, Anthony is gandering at Johanna at Turpin's house. Turpin, enraged by what Anthony has done, orders him out. Nevertheless, Anthony still wants to have Johanna.
Todd and Lovett comes to a barber known as Signor Adolf Pirelli. He challenges him to shave-off and Todd wins. He offers Turpin's henchman, Beadle Bamford, an address of his place.
In his barber store, Todd and Lovett see Pirelli and Toby, his protege, going to his place. He orders her to keep Toby distracted while he deals with Pirelli.
Pirelli greets Todd and reveals his real name: Davy Collins. He orders Todd to give his money back because he entered the shaving contest in a false pretense and that he knows who Todd is. Pirelli tells Todd that he is once used to be his protege and how he remembers Todd's razors, explaining how he ended up discovering Todd's identity. He blackmails Todd into giving his money back or he will tell his secret to the Beadle. Enraged, Todd bludgeons him with a teapot.
By the time Toby arrives, Todd places Pirelli to a trunk. He offers Toby a tot of gin so that he wouldn't go after Pirelli. When Toby leaves, Todd slits Pirelli's throat, killing him.
Meanwhile, Turpin is punishing a young boy by sentence him to be hanged. Outside of court, the Beadle suggests Turpin to shave in order to propose to Johanna.
Lovette goes to Todd's barber shop and asks him how long Pirelli will be back. Todd replies that he won't be back because he killed him. Lovett steals Pirelli's wallet afterwards. When Turpin comes, Todd is about to kill him until Anthony, unaware of Turpin, comes revealing his plot to have sex with Johanna. Angered by that, Turpin leaves and never returning to Todd's shop.
Enraged that Turpin escapes, Todd swears to kill everyone who comes to his shop until he gets to him. Lovett supports him by suggesting of baking pies from people's corpses.
Since then, on one night, Todd turns his chair into a contraption to drop people to Lovett's basement and begins to kill people until he gets to Turpin. Meanwhile, Turpin sends Johanna away to an asylum when she refuses to be with him.
In one day, Todd and Lovett are having a picnic. After the picnic, Anthony reveals to Todd that Johanna is sent in an asylum, giving him an opportunity of sending Turpin to his store and kill him. Todd orders Anthony to get her out and Toby to give a letter to Turpin. Anthony, suspicious of Todd, reluctantly agrees.
At the night, Anthony begins to have suspicions about Todd and after seeing Pirelli's wallet, he thinks that he is murdered and asks Lovett, whom he didn't know that she is involved with the killings, to join him at investigating Todd. Lovett locks Anthony to her basement for Todd to kill him.
In the asylum, Anthony rescues Johanna and leaves a psychiatrist at the mercy of his patients.
The Beadle goes to Todd's shop to investigate about the smoke in the chimney. Todd kills him in front of Toby, getting him scared and hides to the sewers. Todd and Lovett try to find him, but to no avail.
Just then, Anthony leaves Johanna as she hides to a trunk. A beggar woman enters to the shop and recognizes Todd. At the sound of Turpin's voice, Todd kills her and drops her to the basement. Turpin arrives and Todd kills him, but not before he reveals his true identity to him. He finds a disguised Johanna and not recognizing her, prepares to kill her when he hears Lovett screaming. Todd orders Johanna to forget his face and leaves.
In the basement, Lovett is struggling with Turpin. Todd comes and asks her what is she screaming about and Lovett replies that Turpin tries to grab onto her. Todd is about to burn his corpse with the beggar woman. However, he finds out that the beggar woman is his wife, Lucy. Lovett reveals more detail that she is not killed by the poison, but driven insane and becomes a beggar.
Enraged, Todd pretends to forgive Lovett and waltz her maniacally before throwing her to the oven. Todd cradles for his wife when Toby, now knows everything, goes behind him. Knowing this, Todd orders Toby to slit his throat. Toby leaves afterwards.