Figaro and Susanna, the servants of Count and Countess Almaviva, are preparing for their imminent wedding; Susanna reveals that she is being pursued by the Count. Dr. Bartolo and Marcellina conspire to hold Figaro to a contract he made to marry Marcellina if he failed to pay back a loan to Bartolo. The pageboy Cherubino tells Susanna of his love for the Countess, just as the Count arrives. Cherubino hides and overhears Almaviva’s attempted seduction of Susanna. Don Basilio’s arrival forces the Count into hiding as well. The indiscreet Basilio talks of the Count’s love for Susanna and Cherubino’s love for the Countess. The Count emerges from hiding, precipitating a scene that ends with Cherubino ostensibly being packed off by the Count to join the army.

The Countess plots with Susanna to expose her husband’s philandering: Susanna will write the Count agreeing to a rendezvous, but they will send Cherubino in her place, dressed in women’s clothes. As Cherubino is being disguised, the Count arrives and Cherubino hides in a nearby closet. The Count, hearing noises, leaves to fetch tools with which to break open the door. To escape, Cherubino leaps out the window while Susanna takes his place. When the Count returns and finds Susanna in the closet, he is forced to apologize. Figaro arrives, then the irate gardener Antonio, whose flower bed was destroyed by Cherubino’s leap. The Count interrogates Figaro about a mysterious letter, but Figaro evades his questions. Marcellina, Bartolo and Basilio burst in, demanding that Figaro honor the contract for marriage.

Figaro stalls Marcellina by telling her that he is of noble birth and cannot marry without his parents’ consent. He reveals a birthmark on his arm, whereupon Marcellina realizes that she and Bartolo have found their long-lost son. After the Countess has dictated the note that Susanna is to pass to the Count, a double wedding celebration follows – Susanna and Figaro being joined by Marcellina and Bartolo.

Figaro encounters Barbarina, the gardener’s daughter, who inadvertently reveals that Susanna has received a message from the Count. Figaro assumes the worst, and decides to catch his errant wife when she arrives for her tryst in the garden. The Countess and Susanna appear in each other’s clothes (Susanna having taken Cherubino’s place in the subterfuge) and a series of mistaken identities ensures. Figaro eventually realizes his wife is faithful and the Count is publicly embarrassed when he accuses Figaro of romancing his wife, only to find out it is Susanna. Chastened, he begs for the Countess’s forgiveness, which she bestows.