In 1846, Benjamin Barker, Bryn Terfel, a barber, arrives in London with the young sailor, Anthony Hope Jay Armstrong Johnson. A flashback reveals that fifteen years earlier Barker was falsely convicted and exiled to Australia by the corrupt Judge Turpin Philip Quast, who lusted after Barker's wife, Lucy. Barker adopts the alias "Sweeney Todd" and returns to his old shop on Fleet Street, positioned above Nellie Lovett's meat pie shop. Recognizing Barker, Mrs. Lovett Emma Thompson explains that while he was away, Turpin sexually assaulted Lucy and drove her to suicide, then adopted the couple's daughter Johanna as his ward. Todd vows revenge and reopens his barbershop after Lovett, who loves him unrequitedly, presents him with his old straight razors. As he wanders the streets, he encounters a beggar woman, and Anthony becomes smitten with Johanna after seeing her singing by a window high above the street, though Turpin and Beadle Bamford Jeff Blumenkrantz intervene and drive him away.
Rival barber and snake oil salesman Adolfo Pirelli Christian Borle is publicly humiliated by Todd in front of Bamford, but recognizes Todd by his razors and reveals himself as his former apprentice. He attempts to blackmail Todd, who erupts in anger and kills him. Lovett is shocked but accepts Todd's justifications, having grown emotionally attached to Pirelli's downtrodden assistant Toby Ragg Kyle Brenn, whom she adopts as a son.
Intending to marry Johanna, Turpin visits Todd's shop for a grooming at Bamford's recommendation. Before Todd can kill Turpin, Anthony bursts in and inadvertently reveals his plan to elope with Johanna. Turpin flies into a rage, storms out, and has Johanna committed to a madhouse. Believing Johanna is lost to him, Todd vows to kill as many people as he can and seduces Mrs. Lovett into becoming his partner in crime. She proposes baking Todd's victims into pies, and Todd rigs his barber chair with a trapdoor to drop bodies into her bakehouse, while Anthony continues to search for Johanna.
With both their businesses prospering, Mrs. Lovett confides her hopes to marry him and retire, while the unnamed beggar woman begins spreading rumors about the foul-smelling smoke rising from the shop chimneys. Anthony disguises himself as a wig maker to rescue Johanna from the asylum, planning to hide her in Todd's shop. However, Todd sends Turpin a letter about the ploy, prompting Toby to become wary of Todd and warn Mrs. Lovett, who calms him but must lock him in the basement after he discovers Pirelli's purse. Bamford arrives to inspect reports of the stink from the chimney, but Todd tricks and murders him. Mrs. Lovett informs Todd of Toby's suspicions, and the pair search for the boy, who escapes into the sewers. Meanwhile, Anthony brings Johanna, disguised as a boy, to the shop and has her wait there while he goes to find Todd.
The beggar woman enters the shop in search of Bamford, and Johanna hides in the trunk. The woman recognizes Todd, asking, > "Do I know you?" <, but upon Turpin's arrival, Todd kills her and sends her through the trapdoor. Todd explains to Turpin that Johanna has repented and is coming to him, offering a free shave in the meantime. He then reveals himself as Benjamin Barker, before slashing Turpin's throat and dropping him into the bakehouse.
Todd finds Johanna but does not recognize her at first, planning to kill her as well. The dying Turpin grabs Mrs. Lovett's dress, causing her to scream and distract Todd; he allows Johanna to flee and rushes to the bakehouse to finish the job. When he finally recognizes the beggar woman as his wife Lucy, he realizes Mrs. Lovett lied about her death and hurls her into the oven. Toby reappears and slits Todd's throat with his own razor as he bleeds over the body of his dead wife.
