The action unfolds now in the garden of the castle where abound groves and bowers.
 
Barberina is troubled, following the instructions of the note, the Count sent her to carry the pin to Suzanne but the young girl lost it "I lost it... poor me". (Cavatina "L'ho perduta"). Figaro teases Barberina but this story of pin worries him. Wouldn't Susanna have already succumbed to the Count's assaults by accepting this rendez-vous? He confides his fears to his mother Marcellina who doubts Susanna’s duplicity "only we poor women are always treated with cruelty by these perfidious men" (Aria: "Il capro e la capretta").
 
There follows a dialogue between Figaro, Bartolo and Basilio who recognizes that "in this world, rubbing shoulders with the great is always dangerous, ... but to survive, the little people, can escape shame, perils and death ... in front of a ferocious animal, a donkey skin may suffice" (Aria: "In quegl' anni, in cui val poco").
 
Figaro is left alone, he decides to take revenge and to confound the lovers in front of exeryone "everything is ready", cursing the female gender "Ah, trusting women is madness! Open your eyes imprudent and stupid men" (Recitative and aria : "Tutto e disposto - Aprite un po'quegl'occhi").
 
At the approach of the Countess and Susanna (who have exchanged their clothes) Figaro hides to listen to them. Susanna, who has been warned by Marcelina, also wants to play a trick on Figaro who dares to doubt her fidelity. "The rascal is on sentry, let's entertain ourselves, let's make him pay for his suspicions", she sings her hope to find her beloved "The moment has come to be happy in the arms of the one I love" (Air "Giunse alfin il momento...Deh vieni, non tardar ")[2]
 
The rendez-vous is approaching, the comedy of the false identities can begin. The night is favourable to misunderstandings: Cherubino undertakes to seduce the one he believes to be Susanna but who is in reality the Countess. The false Susanna resists him. Cherubino attempts a kiss which is received by the Count who has come to intervene. The slaps rain down, Cherubino decamps leaving the Count alone with his false Susanna. It is now up to the Count to court the false Susanna and to offer her a beautiful ring as a token of love.
 
The Count flees and it is around Susanna under the clothes of the Countess to try to seduce Figaro. Figaro is drunk with anger but having recognized Susanna's voice understands the trick and, after having entered into her game by becoming more and more enterprising, confesses to her having recognized her. The newlyweds make peace and launch into a great love scene "Let's run my love and let the pleasure compensate the pain!”.
 
But Suzanna is still in the clothes of the Countess and the Count, believing to see his adulterous wife in the arms of a gallant, emerges from a bush and calls his people, determined to punish the guilty. He brings out of the bushes one by one Cherubina, Barbarina, Marcellina and the presumed guilty.
 
The masks fall to the great confusion of the Count when the true Countess appears. The Count has no other solution than to implore the forgiveness of his wife. She accepts his apology, the couples reform for the finale "Contessa perdono... Questo giorno di tormenti" and the opera ends in general rejoicing "Thus we are all happy, only love could conclude this day in joy and gladness".