It is dawn in Seville. Count Almaviva is in love with Rosina, the ward of Doctor Bartolo. The Count serenades the young woman, but she fails to come to her window. Figaro, barber and jack-of-all-trades, enters to offer his help. Bartolo emerges, and Figaro and Almaviva overhear his plans to marry Rosina himself. Almaviva serenades her again, introducing himself as a poor student named Lindoro, not wanting Rosina to marry him for his rank. She briefly responds before the shutters are abruptly closed. Figaro concocts a plan to get the Count into her house disguised as a drunken soldier.
Inside the house, Rosina has written a love letter to Lindoro. She asks Figaro for help, but their conversation is interrupted by the entrances first of Doctor Bartolo and then by her music teacher, Don Basilio. Don Basilio warns Bartolo that a certain Count Almaviva has arrived in town and is interested in Rosina. He advises the doctor to spread slanderous rumors about the Count to drive him out of town. Bartolo replies that he would rather marry Rosina that very day and the two men go off to draft the contract.
Figaro tells Rosina of “Lindoro,” and she gives him the letter she had already written to her unseen lover. Bartolo returns, suspecting something is wrong. The Count enters, pretending to be a drunken soldier with orders to lodge in Bartolo’s house. In the ensuing uproar, Almaviva slips Rosina a note. The commotion attracts the attention of the police, who attempt to arrest Almaviva. The Count takes the sergeant aside and quietly informs him of his noble rank. Almaviva is immediately released, dumbfounding everyone.
The Count again enters Bartolo’s house, now claiming to be Don Alonso, a substitute music teacher for Rosina. Bartolo is suspicious, but Almaviva tricks him into thinking he is his ally. Rosina enters and the two proceed with their “music lesson” while Bartolo dozes. Figaro arrives to shave Bartolo, in the process obtaining the key to the balcony so the lovers can escape that night. Basilio enters and almost exposes Almaviva as a fake, but the Count bribes Basilio to feign sickness and remain silent. Bartolo finally realizes he is being duped and angrily orders the doors guarded. Berta, Bartolo’s housekeeper, comments on the foolishness of old men wishing to marry young women.
Bartolo tricks Rosina into thinking her “Lindoro” is merely a go-between for Count Almaviva, whom he falsely describes as a villain. In her disappointment, she agrees to marry Bartolo. As a storm rages outside, Figaro and Almaviva enter, and the Count reveals his true identity to the delighted Rosina. They express their love while Figaro urges them to get out of the house.
By the time they try to escape, their ladder has disappeared. Basilio enters with a notary. Once again, the Count bribes Basilio to remain quiet, and Figaro instructs the notary to marry Almaviva and Rosina. Bartolo bursts in with the guards, but it is too late. Almaviva reveals his identity to the doctor. Bartolo, relieved that he can keep Rosina’s dowry, resigns himself. All wish the couple eternal love and fidelity, while Figaro pronounces the quintessential thesis: “The scoundrels have all the luck in this world.”