It is 1845, and Anthony, a young sailor, has just arrived home to London. He is accompanied by a man he rescued drowning off the coast of Australia, Sweeney Todd. As they disembark, they are accosted by a beggar woman who alternates between begging for alms and soliciting sex, but seems to recognize Sweeney.
Anthony is thrilled to have return to London, but Sweeney is not—he tells Anthony the tale of a young barber who was sent into exile by a powerful man with designs on the barberʼs beautiful wife. Sweeney enters a pie shop on Fleet Street, and is immediately accosted by the owner Mrs. Lovett. She bemoans the hard times, and the scarcity of meat (and the speedy cats). Sweeney asks about the empty apartment upstairs, and Mrs. Lovett tells him about the barber Benjamin Barker and who was falsely accused by Judge Turpin so that the Judge could get Barkerʼs wife, Lucy. The Judge and Bedle Bramford lured Lucy to the Judgeʼs house so he could torment and rape her. Sweeneyʼs anger confirms what Mrs. Lovett had suspected – that he is indeed Benjamin Barker.
Mrs. Lovett tells Sweeney that Lucy had poisoned herself, and that his daughter Johanna was now a ward of Judge Turpin. Mrs. Lovett returns a set of silver shaving razors to Sweeney, who vows to use them to get his revenge. In Judge Turpinʼs house, Johanna sits at a window. Anthony happens to wander by and immediately falls in love with the beautiful young woman. Threats from the Beedle only strengthen his resolve to save her.
Barber Signor Pirrelliʼs assistant Tobias hawks a miracle elixir that regrows hair. After exposing the elixir as a hoax, Sweeney challenges Pirrelli to a shaving contest, which Sweeney wins easily. Beadle Bamford judged the contest and is impressed—Sweeney invites him to come in for a complimentary shave. Anthony, not knowing that Johanna is Sweeneyʼs daughter, asks the barber for help—he intends to rescue Johanna, and wants to use the shop as a safe house. Pirelli arrives to pay Sweeney a visit. Mrs. Lovett takes Toby downstairs for a pie, and Pirelli drops the accent and reveals that he used to be Benjamin Barkerʼs assistant. Instead of giving in to blackmail, Sweeney kills Pirelli.
Johanna is terrified because the Judge intends to marry her on Monday, but Anthony has a plan to help her escape. Meanwhile, the Beadle suggests that the Judge clean up a bit to be more attractive to Johanna, and sends him to Sweeny Todd. As the Judge tells Sweeney about his impending marriage, Sweeney shaves him, enjoying the anticipation of his revenge. But before he can slit the Judgeʼs throat, Anthony bursts in and blurts out his plan to save Johanna. The Judge storms out, declaring that he will lock Johanna up and never come to the barber shop again. Sweeney swears to kill as many people as possible, punishing the rich and corrupt and freeing the poor from their saddened state. Mrs. Lovett sees an opportunity—they can dispose of the bodies by using the meat for her pies—and so a new enterprise is born
Mrs. Lovettʼs pie shop is now bustling, and Toby helps with customers. Sweeney has a brand new chair, with some special modifications. When Anthony discovers that the Judge has locked up Johanna in the asylum, he gets Sweeney to help him plan an escape—Anthony will go to the asylum pretending to be a wigmaker looking for hair from the inmates. Seeing an opportunity to lure the Judge back to his shop, Sweeney writes a letter, warning him of Anthonyʼs plan, and that Anthony and Johanna could be captured at the barber shop.
Toby has begun to suspect that there is something awry at the pie shop, and tries to warn Mrs. Lovett. Mrs. Lovett distracts him and sends him down into the bakehouse. She returns upstairs to find the Beadle waiting— he has been sent to investigate the strange smells and smoke coming from her chimneys. Sweeney comes in and offers the Beadle his free shave. Toby is still in the basement when the Beadleʼs body tumbles down, and he runs off.
The asylum owner Fogg tries to stop Anthony from rescuing Johanna. She shoots Fogg, leaving the rest of the inmates to wander through the streets of London, as Sweeney and Mrs. Lovett search for Toby. Back at Sweeneyʼs shop, Johanna hides to avoid the beggar woman, and Anthony goes looking for Sweeney. When Sweeney arrives and finds the beggar woman in his parlor, he slits her throat. The Judge arrives, and Sweeney lures him into the chair before revealing his true identity and killing the Judge. Johanna comes out of hiding and barely escapes Sweeneyʼs knife.
Mrs. Lovett struggles with the bodies in the basement. Sweeney arrives, and in the ovenʼs light finally recognizes the beggar woman—it is his wife Lucy. Mrs. Lovett only let him assume that the poison killed his wife out of love, and Sweeney takes Mrs. Lovett in his arms for a dance, but then shoves her into the oven.
Sweeney kneels on the floor, holding Lucy. From behind him, a white-haired Toby approaches and slits Toddʼs throat just as Johanna, Anthony, and the police enter.