The young Rosina is under the careful watch of her guardian, Dr. Bartolo, who intends to marry her in order to maintain control over her dowry. She has attracted the attention of Count Almaviva, who is presently disguised as a poor student, Lindoro, in order to determine if her love is reciprocal and genuine. He employs a small group of musicians to serenade at Rosina’s window, but she does not appear. Instead the count encounters Figaro, the town factotum of many indispensable talents and formerly in his employ. The count describes his predicament and (for a price) Figaro offers to help – because he has access to Bartolo’s household as his barber, he might be useful in winning Rosina’s release for the count. Rosina appears at the window with a letter in hand but is apprehended by the jealous doctor. She lets the letter drop, and while Bartolo runs down to retrieve it, beckons to “Lindoro” to pick it up. When Bartolo finds no letter, Rosina insists that the wind must have blown it away, but he remains suspicious. Figaro devises a plan to have the count gain entrance to the house by disguising himself as a drunken soldier. Once inside, he will be able to meet with his beloved.
Inside Bartolo’s house Figaro briefly confers with Rosina, who is determined to outwit her jailer. The sound of Bartolo approaching puts Figaro into hiding. The doctor enters in a fury – Figaro has debilitated his household staff by administering all the wrong medicines. When accused, Rosina admits to speaking to him and curtly leaves the room. Bartolo receives a visit from Rosina’s music teacher, Don Basilio, who brings news that Count Almaviva is in Seville and traveling incognito in order to court Rosina undetected. Basilio advises Bartolo to destroy his rival by spreading vicious rumors. Bartolo decides instead to marry Rosina quickly, and they exit as Basilio agrees to help with the wedding arrangements.
Figaro, who has been listening the entire time, finds Rosina to tell her of Bartolo’s plot and to let her know of her mystery lover’s imminent visit. Rosina is overjoyed, and at Figaro’s suggestion, begins to write “Lindoro” a note. Figaro leaves as Bartolo returns. He accuses Rosina of writing secret letters – a doctor of his standing cannot be easily fooled. He is determined to keep her under lock and key until their marriage is finalized.
Dressed in his soldier’s disguise, Almaviva arrives at Bartolo’s house and gives the doctor a written order requiring that he is to be given a night’s lodging. Bartolo desperately protests that he has an exemption from such billeting. Meanwhile, Rosina attempts to retrieve a letter from the count but once observed, tries to convince Bartolo that it is a laundry list. As the pandemonium grows, the police are summoned, but an attempt to take Almaviva into custody is aborted as he privately reveals his true identity to the sergeant. It seems everyone, especially Dr. Bartolo, is left completely confounded by the day’s events.
The count has assumed the new disguise of Don Alonso, a music teacher, in his continuing effort to win a few moments with Rosina and eventually free her from the household prison. Bartolo is made to believe that he is a student of Don Basilio and has been sent in his place because the music master is ill. He then gains Bartolo’s confidence by telling him he is privy to the plan to defame the count and hands him Rosina’s letter as further evidence of his complicity. Bartolo falls for the story and allows the lesson to begin. Figaro enters, and while preparing for the doctor’s shave, takes the opportunity to steal the key to Rosina’s balcony. He creates a diversion to temporarily lure Bartolo away, and Rosina and Almaviva (whom she still believes to be Lindoro) discuss the details of their nocturnal escape. The unexpected arrival of Basilio complicates the matter, but sufficiently bribed, he is quickly ushered away. Bartolo eventually overhears details of the lovers’ plot and orders “Don Alonso” from his house.
Realizing the count’s agents have penetrated his home, Bartolo is determined to marry Rosina at once. He shows her the letter to Lindoro, claiming he obtained it from Count Almaviva, for whom Lindoro must be working. Rosina is left alone to consider her betrayal as a storm rages outside. As night falls, Figaro and Almaviva appear on the balcony as planned but are confronted by a furious Rosina, who believes she has been deceived. Almaviva reveals his true identity, and Rosina, at first stunned, accepts him with joy. Along with Figaro, they plan a big surprise for Bartolo upon his return.