Figaro and Susanna, servants to the Count and Countess Almaviva, are preparing for their wedding. Figaro is furious when he learns from his bride that the Count has tried to seduce her. He’s determined to have his revenge on his master.
Dr. Bartolo appears with his former housekeeper, Marcellina, who is equally determined to marry Figaro. She has a contract: Figaro must marry her or repay the money he borrowed. When Marcellina runs into Susanna, the two rivals exchange insults.
Susanna returns to her room and an adolescent boy, Cherubino, rushes in. Finding Susanna alone, he tells her he loves her — and every other woman in the house. The Count appears, again trying to seduce Susanna, and Cherubino hides. The Count then conceals himself as well when Basilio, the music teacher, approaches. Basilio tells Susanna that Cherubino has a crush on the Countess. This causes the Count to step forward in anger. He becomes even more enraged when he discovers Cherubino and realizes that his attempts to seduce Susanna have been overheard.
He chases Cherubino into the great hall where they are met by Figaro, who has assembled the entire household to sing the praises of their master. The Count is forced to bless the marriage of Figaro and Susanna. To spite them and to silence Cherubino, he orders the boy to join the army without delay. Figaro ironically tells Cherubino what to expect in the army — no flirting with girls, no fancy clothes, no money, just shells, cannons, bullets, marching, and mud.
In her bedroom, Rosina, the Countess, mourns the loss of love in her life. Encouraged by Figaro and Susanna, she agrees to set a trap for her husband: they will send Cherubino, disguised as Susanna, to a rendezvous with the Count that night and at the same time make him believe that the Countess is having an assignation with another man. Cherubino appears and the two women lock the door, then begin to dress him up as a girl. While Susanna steps into an adjoining room, the Count knocks and is annoyed to find the door locked. Cherubino shuts himself in the dressing room and the Countess lets her husband in. When there’s a sudden noise from the dressing room, the Count skeptical of his wife’s story that Susanna is in there.
Taking his wife with him, he leaves to get tools to force the door. Meanwhile, Susanna, who has re-entered the room unseen and observed everything, helps Cherubino escape through the window before taking his place in the dressing room. When the Count and Countess return, both are astonished to find Susanna in there. All seems well until the gardener, Antonio, appears, complaining that someone has jumped from the window, ruining his flowers. Figaro, who has rushed in to announce that everything is ready for the wedding, improvises quickly, feigning a limp and pretending that it was he who jumped. At that moment Bartolo, Marcellina, and Basilio arrive, putting their case to the Count and waving the contract that obliges Figaro to marry Marcellina. Delighted, the Count declares that Figaro and Susanna’s wedding will be postponed.
Later in the day in the great hall, Susanna leads the Count on with promises of a rendezvous that night. He is overjoyed but then overhears Susanna conspiring with Figaro. In a rage, he declares he will have revenge.
The Countess, alone, recalls her past happiness. She’s determined to go through with the conspiracy against her husband, and she and Susanna compose a letter to him confirming the rendezvous with Susanna that evening in the garden under the pine trees.
Marcellina, supported by a lawyer, Don Curzio, demands that Figaro pay his debt or marry her at once. Figaro replies that he can’t without the consent of his parents for whom he’s been searching for years, having been abducted as a baby. When he reveals a birthmark on his arm Marcellina realizes that he is her long-lost son, fathered by Bartolo. Seeing Figaro and Marcellina embrace, Susanna thinks her fiancé has betrayed her, but she is pacified when things are explained.
Cherubino, now dressed as a girl, appears with his girlfriend, Barbarina, the daughter of Antonio. Antonio, who has found Cherubino’s cap in the garden, also arrives and unmasks the young man. The Count is furious to discover that Cherubino has disobeyed him and is still in the house. But his anger is punctured by Barbarina—who reveals that the Count, when he attempted to seduce her, promised her anything she wanted. What she wants now is to marry Cherubino. The Count is forced to agree. A march is heard and the household assembles for Figaro and Susanna’s wedding. While dancing with the Count, Susanna hands him the letter, sealed with a pin.
At night in the garden, Barbarina is in despair: she has lost the pin that the Count has asked her to take back to Susanna. When Figaro and Marcellina appear, Barbarina tells them about the planned rendezvous between the Count and Susanna. Thinking that his bride is unfaithful, Figaro rants against all women. He hides when Susanna and the Countess arrive, dressed in each other’s clothes. Alone, Susanna sings of love. She knows that Figaro is listening and enjoys making him think that she’s about to make love to the Count. Then she also conceals herself—in time to see Cherubino try to seduce the disguised Countess. The boy is chased away by the Count who wants to be alone with the woman he believes to be Susanna. Figaro, by now realizing what is going on, joins in the joke and declares his passion for Susanna in her Countess disguise. The Count returns. Finding Figaro with his wife, or so he thinks, he explodes with rage. At that moment, the real Countess steps forward and reveals her identity. Ashamed, the Count asks her pardon. After many moments of agonizing doubt, she forgives him and both couples are reunited.