As the opera begins, Susanna and Figaro are examining the room which they will occupy after their marriage. Figaro notes that its convenient location, adjoining the boudoir of the Countess, should make it possible for Susanna to be readily available to the Countess when needed. Susanna, on the other hand, notes that it is also an easy matter for the Count to get to her if Figaro is away. Figaro resolves to stop the Count’s pursuit. As he leaves, Dr. Bartolo enters, explaining to Marcellina how he will use his legal knowledge to trap Figaro into marrying the former duenna.

Cherubino, recently dismissed by the Count for having been discovered in an escapade with Barbarina, begs Susanna to plead his case before the Countess. When voices are heard outside the door, Susanna conceals the page and admits the Count whose advances are, in turn, interrupted by the entrance of Don Basilio. The Count also is forced to hide, but reveals himself when he hears of gossip concerning the Countess and Cherubino. Upon discovering that the page has been concealed in the room and has therefore overheard the entire conversation, the Count decides to rid himself of Cherubino by giving him a commission in his regiment.

Act II introduces the Countess who regrets the loss of her husband’s love. Figaro and Susanna explain their plan to embarrass the Count into marital fidelity: The Count will be given an assignation with Susanna, but her place will be taken by Cherubino in disguise; then the Count will be sent an anonymous letter telling him that the Countess, in revenge, has made a rendezvous with an unknown man. Just as Cherubino is dressed, the Count knocks on the door. Cherubino hides in a closet. Susanna, who had gone to her room for a moment, returns to overhear the argument between Count and Countess. When the Count leaves to get tools to break down the door, Susanna exchanges places with Cherubino who escapes through a window. The Count is mystified to find Susanna in the room and interrogates Figaro who denies all knowledge. Suddenly the gardener bursts in, protesting that his flower beds have been ruined by a man jumping from the window. Figaro attempts to take the blame but is interrupted by the entrance of Marcellina, accompanied by Bartolo and Basilio, who has come to lodge a formal complaint of breach of promise.

Act III begins with Susanna agreeing to meet the Count that night. Leaving, she meets Figaro and assures him that he will win his case against Marcellina. Overhearing their conversation, the Count is furious. At the hearing, he is quick to render judgment in Marcellina’s favor until it is discovered that Figaro is the natural son of Marcellina and Dr. Bartolo.

The Countess muses on the past and permits herself to hope that her own fidelity will result in a return of the Count’s affection. She and Susanna write a letter to the Count, naming a meeting place for the evening’s rendezvous. A group of village girls comes to present bouquets to the Countess. The Count, warned by Antonio of the presence of Cherubino, discovers the disguised page in the group. Barbarina saves the situation by asking the Count to give her Cherubino as her husband. Susanna and Figaro are finally wed, and during the ceremony, Susanna slips the Count the letter which she and the Countess had written.

Act IV unties all the knots. Unknown to Figaro, the Countess and Susanna have exchanged clothing, and he is enraged to see Cherubino and the Count in tête-à-tête with “his wife” (in reality the Countess). Figaro suddenly sees through the disguise and makes love to Susanna as if she were the Countess. Susanna forgives the joke and the two join forces against the Count. Pleading with the angry Count is in vain until the Countess herself is heard. Realizing that he has been duped, the Count begs forgiveness of his wife and the opera ends amid general rejoicing.