A room in the palace between the apartments of the Count and the Countess (early morning). Figaro, the barber who helped Count Almaviva win the hand of Rosina in Rossini’s The Barber of Seville, is now valet in the Count’s household and preparing to wed the Countess’s maid, Susanna.

The Count has designs on Susanna and has given the couple a room near his own quarters. Figaro determines to thwart any hanky-panky, but first there is a blackmail scheme he must evade—marriage to Dr. Bartolo’s housekeeper, Marcellina—and the lovesick young page Cherubino to protect from the Count’s wrath. Cherubino seeks Susanna’s help but swiftly hides when the Count comes a-courting. The Count in turn has to hide when interrupted by the music master, Don Basilio, but comes forward when he hears Basilio insinuate that Cherubino is sweet on the Countess. Now really in hot water, Cherubino is momentarily saved when Figaro leads in a delegation of peasants who’ve come to salute the Count for abolishing the custom of droit du Seigneur, an old custom giving landowners the first night with any bride among his retainers. To be rid of Cherubino the Count appoints him to his regiment.

The Countess’s boudoir (forenoon). Figaro and Susanna conspire with the Countess to trick the Count. They will dress Cherubino as Susanna for a rendezvous with the Count. The Count interrupts their preparations, however, and Cherubino hides next door. He manages to escape by jumping from the window, and Susanna quickly takes his place before the Count can get the door unlocked. Figaro, coming to collect the ladies for the wedding ceremony, covers up for Cherubino but then finds himself trapped by Dr. Bartolo and Marcellina’s false matrimonial demands. The Count postpones the wedding until he can study the case.

A hall in the palace (afternoon).  The Countess, who longs to regain her husband’s love, schemes with Susanna to engineer a tryst with the Count in the garden at night. The Count’s plan to force Figaro’s marriage to Marcellina is thwarted when it is discovered that Marcellina and Dr. Bartolo are actually Figaro’s parents.

The Countess resolves to expose the Count by dictating a love letter to him from Susanna, including a pin, which is to be returned as his reply.

The Count is forced to hold a double wedding: Figaro and Susanna; Dr. Bartolo and Marcellina.

The park of the palace (evening).  Susanna and the Countess exchange dresses and pretend to be one another. Both the Count and Cherubino pay court to “Susanna,” actually the Countess. At first Figaro misunderstands, thinking Susanna is betraying him. But once he realizes the game, he plays along and woos “the Countess” to irritate Susanna. The Count is incensed by what he takes to be his wife’s infidelity and calls upon the others to join in condemning her. Finally, the real Countess reveals her identity and accepts the Count’s plea for forgiveness, whereupon the four couples — Figaro and Susanna, the Count and Countess, Cherubino and Barbarina, and Dr. Bartolo and Marcellina— celebrate the end of “the day of madness.”