Prior to the action of the opera: The Barber of Seville
Figaro, a barber and general factotum well known in Seville, has aided his former employer, Count Almaviva, to woo and win Rosina, ward to Bartolo, an elderly doctor. Bartolo had no great love for the girl but did have designs upon her substantial dowry. Figaro's machinations have left Bartolo feeling angry and vengeful.

Count Almaviva, in his gratitude, has once again retained Figaro's services as valet. It is now three years after the whirlwind courtship and marriage of Count Almaviva and Rosina. Figaro has fallen in love with Susanna, Rosina's chambermaid.

Act I: A storage room in the palace of Count Almaviva near Seville:
On their wedding morning Susanna tries on her veil while Figaro measures their new room for a bed, given to them by the count. Susanna, chaffing at the implication that the count is a generous master, points out to Figaro the direct correlation of the proximity of their room to his, adding further that their employer has made his romantic interest in her very plain. Further, it appears that the count plans to reinstate his droit du seigneur, a medieval tradition abolished on the occasion of his own wedding to Rosina. This feudal right entitles him to sleep with any new bride in his employ before her husband does. Susanna is called away by the countess, and the now-furious Figaro plots revenge.

Revenge of a more long-standing kind is, meanwhile, being concocted by Bartolo. His old housekeeper, Marcellina, has an outstanding promissory note from Figaro, the collateral upon which is Figaro's consent to become the old spinster's husband. Marcellina, with Don Bartolo as her legal advisor, has decided to sue Figaro for repayment or matrimony, and they both agree that the count's sexual interest in Susanna will place him firmly on their side when he comes to decide the case.

Cherubino, pageboy to the count, in love with every woman he sees (but especially Countess Almaviva) confides his overwhelming emotional state to Susanna, but their conversation is interrupted by the unexpected arrival of the count. Already in trouble with Almaviva for being caught in a compromising situation the previous day, Cherubino hides. While hidden he manages to overhear a conversation in which the count tries to pay Susanna for sexual services rendered. Cherubino's presence is revealed, but before punishment can be fully carried out, Figaro arrives with a group of peasants rehearsed to over-praise the count's magnanimity in abolishing his droit du seigneur.

Figaro invites the count to bless the purity of the impending nuptials, but the count, anticipating the arrival of Marcellina, defers his blessing to a later time. Quickly appointing Cherubino to the post of regimental captain (in a regiment far from the palace), he departs, leaving Figaro to describe the pleasures and pains of military life to the new soldier.

Act II: The countess' room
Clearly unhappy that her husband's attentions have turned to other women, the countess questions Susanna about the recent scene with the count. Figaro, meanwhile, has worked out a plot in which Cherubino, dressed as Susanna, could entrap the count that evening in the garden, thus exposing his lechery. The countess nervously agrees to Figaro's plan, but  while she and Susanna are in the act of creating the boy's female disguise, the count returns unexpectedly from a hunting trip. Cherubino, terrified at the prospect of being caught by the count in suspicious circumstances yet again, locks himself in a closet where he is unable to remain quiet. Alerted by the noise within, the count is convinced that his wife is concealing a lover. Determined to force the door open if he has to, the count takes the countess with him on his search for tools. He locks the door behind them to prevent unwanted entrances or exits. Susanna, having hidden herself from the count, persuades Cherubino to open the door, but as they are both still trapped in the main room, Cherubino heroically jumps out of the window and runs away. Susanna takes his place in the closet, and before the count can force open the door, she surprises both him and his wife by her presence. Baffled, the count is appropriately embarrassed. Just on the point of resolution, however, the situation is upset again: first by Antonio the gardener (who has seen Cherubino jump from the window), then by Marcellina, Bartolo, and the meddlesome music master, Basilio, all of whom arrive to press Marcellina's suit against Figaro.

Act III: The count's study and, later, a large hall in the palace
Susanna tells the count that she has changed her mind and will accept his offer. The money he gives her in exchange for her affections can, she says, be used against Marcellina's claim on Figaro. Delighted, the count insists that they meet in the garden later that evening, but his triumph is cut short when he overhears Susanna tell Figaro that the case (against Marcellina) has been won without a trial. Rightly convinced that he has been tricked by his servants, the count angrily resolves not to be outwitted. The countess is eager to hear from Susanna about her appointment with the count. Reflecting on her unsuccessful marriage and her desire for it to be otherwise, she feels further humiliation by the fact that she has had to turn to her servants for assistance in such a personal matter.

The argument between Marcellina and Figaro is finally heard by Count Almaviva and Don Curzio, a judge, and despite Figaro's glibness, the decision seems clearly to have gone in Marcellina's favor. Figaro, claiming that he cannot marry without his parents' consent, reveals his childhood status as a foundling. In a sublime moment of feminine intuition, Marcellina questions him about the circumstances of that status. Within seconds, it is revealed to the astonishment of all assembled that Figaro is, in fact, Marcellina's son, Rafaello; further that his heretofore unknown father is none other than his nemesis, Bartolo. Case closed. Susanna stumbles into the middle of these revelations with a purse of money from the countess, given to her to pay off Marcellina. At first she is upset by Figaro's affection toward Marcellina, but her irritation soon turns to joy. Their new wealth is augmented first by Marcellina's cancellation of her debt and then by an unexpected cash gift from Bartolo. Marcellina determines that she and Bartolo will finally legalize their own, somewhat ancient, union by joining Figaro and Susanna in a double wedding.In spite of his inability to stop the wedding, however, the count still plans to have Susanna, and the countess knows it. Finally taking matters into her own hands, she dictates to Susanna an invitation to the count. That night, while the wedding festivities take place within, the palace garden will become the site of a seduction scene: that of an unfaithful husband to his own wife, disguised as her lady-in-waiting.

ACT IV: The garden of the palace
Barbarina, Antonio's pretty daughter, is found searching the garden for the pin the count has dropped off the note that Susanna gave him during the wedding ceremony. She tells her troubles to Figaro, who immediately believes that Susanna is, after all, preparing to meet the count. He offers a diatribe against women, then hides so that he may catch Susanna in her tryst with Almaviva.

Susanna and the countess arrive. Knowing that Figaro is listening, Susanna sings ambiguously of the approach of romantic bliss. Except for a near-disaster with Cherubino, the assignation goes, more or less, as planned, and the count woos his wife thinking that she is Susanna. Figaro recognizes Susanna in disguise as the countess, but pretends not to; dramatically he makes a play for her. Susanna realizes Figaro's joke at her expense, and the two of them purposely throw themselves in the path of the count so that he can catch "his wife" in a compromising situation with Figaro. Furious, the count berates the supposed countess only to have the real countess, still dressed as her servant, offer intercession. Chagrined, humiliated, and yet overcome with love for the woman he married, the count begs for, and is granted, the pardon of the countess.