In 1846, Benjamin Barker, a barber, arrives in London, accompanied by sailor Anthony Hope. Fifteen years earlier, he was falsely convicted and exiled by the corrupt Judge Turpin, who lusted after Barker’s wife Lucy. Barker adopts the alias “Sweeney Todd” and returns to his old Fleet Street shop, situated above Mrs. Nellie Lovett’s meat pie shop, where she sells the “worst pies in London”. Lovett tells him that Turpin raped Lucy, who then poisoned herself with arsenic. The couple’s daughter, Johanna, is now Turpin’s ward. Todd vows revenge, and re-opens his barber shop after Mrs. Lovett, who loves him unrequitedly, presents him with his old straight razors. Anthony becomes enamored with Johanna, but is caught by Turpin and driven away by his henchman, Beadle Bamford.
Todd denounces faux-Italian barber Adolfo Pirelli’s hair tonic as a fraud and humiliates him in a public shaving contest judged by Bamford. A few days later, Pirelli arrives at Todd’s shop, with his boy assistant Tobias Ragg. Pirelli identifies himself as Todd’s former assistant, Davy Collins, and threatens to reveal Todd’s secret unless Todd gives him half his earnings. Todd kills Collins, and hides his body in a trunk.
After receiving advice from Bamford, Turpin visits Todd for grooming, intent on marrying Johanna. Todd shaves Turpin, preparing to slit his throat; they are interrupted by Anthony, who reveals his plan to elope with Johanna before noticing Turpin. An angered Turpin renounces Todd’s service and leaves. Todd swears revenge on the entire world, vowing to kill as many people as he can while he waits for another chance to kill Turpin. Mrs. Lovett gets the idea to bake Todd’s victims into pies, and Todd rigs his barber chair to drop his victims’ bodies through a trapdoor and into her bakehouse. Anthony searches for Johanna, whom Turpin has sent to an insane asylum upon discovering her plans to elope with Anthony.
The barbering and pie-making businesses prosper, and Mrs. Lovett takes Toby as her assistant. She tells an uninterested Todd of her plans to marry him and move to the seaside. Anthony discovers Johanna’s whereabouts and, following Todd’s suggestion, poses as a wigmaker’s apprentice to rescue her. Todd has Toby deliver a letter to Turpin, telling him where Johanna will be brought when Anthony frees her. Toby has become wary of Todd and tells Mrs. Lovett of his suspicions, vowing to protect her.
Bamford arrives at the pie shop, informing Mrs. Lovett that neighbors have been complaining of the stink from her chimney. Todd distracts him with an offer of a free grooming and murders him. Mrs. Lovett informs Todd of Toby’s suspicions, and the pair search for the boy, who is now hiding in the sewers after finding human remains in Mrs. Lovett’s bakehouse. Meanwhile, Anthony brings Johanna, disguised as a sailor, to the shop, and has her wait there while he leaves to find a coach.
A beggar woman enters the shop in search of Bamford, and Johanna hides in the trunk. The woman recognizes Todd, but upon hearing Turpin coming, Todd kills her and sends her through the trapdoor in the floor. As Turpin enters, Todd explains that Johanna had repented and is coming to him, then offers a free shave in the meantime. When Turpin finally recognizes Todd as Benjamin Barker, Todd stabs him several times, cuts his throat, and dumps him into the bakehouse. Johanna comes out of her hiding place, still in disguise, and Todd prepares to kill her as well, not recognizing her as his daughter. However, hearing Mrs. Lovett scream in horror in the basement when the dying Turpin grabs at her dress, Todd spares Johanna.
Todd discovers that the beggar woman was his wife Lucy, whom he believed to be dead, and that Mrs. Lovett deliberately misled him so she could have him to herself. Todd pretends to forgive her and dances with her before hurling her into the bakehouse oven, then cradles Lucy’s dead body in his arms. Toby appears, enraged at Mrs. Lovett’s death, and Todd allows Toby to slit his throat with his own razor. Toby leaves as Todd bleeds to death over his dead wife.