Place: Seville, Spain
Time: 18th century

Act 1
The square in front of Bartolo's house

In a public square outside Bartolo's house a band of musicians and a poor student named Lindoro are serenading, to no avail, the window of Rosina ("Ecco, ridente in cielo"; "There, laughing in the sky"). Lindoro, who is really the young Count Almaviva in disguise, hopes to make the beautiful Rosina love him for himself – not his money. Almaviva pays off the musicians who then depart, leaving him to brood alone. Rosina is the young ward of the grumpy, elderly Bartolo and she is allowed very little freedom because Bartolo plans to marry her once she is of age and thus appropriate her not inconsiderable dowry.

Figaro approaches singing (Aria: "Largo al factotum della città"; "Make way for the factotum of the city"). Since Figaro used to be a servant of the Count, the Count asks him for assistance in helping him meet Rosina, offering him money should he be successful in arranging this. (Duet: "All'idea di quel metallo"; "At the idea of that metal"). Figaro advises the Count to disguise himself as a drunken soldier, ordered to be billeted with Bartolo, so as to gain entrance to the house. For this suggestion, Figaro is richly rewarded.

A room in Bartolo's house with four doors

The scene begins with Rosina's cavatina, "Una voce poco fa" ("A voice a little while ago"). (This aria was originally written in the key of E major, but it is sometimes transposed a semitone up into F major for coloratura sopranos to perform, giving them the chance to sing extra, almost traditional, cadenzas, sometimes reaching high Ds or even Fs.)

Knowing the Count only as Lindoro, Rosina writes to him. As she is leaving the room, Bartolo and Basilio enter. Bartolo is suspicious of the Count, and Basilio advises that he be put out of the way by creating false rumours about him (this aria, "La calunnia è un venticello" – "Calumny is a little breeze" – is almost always sung a tone lower than the original D major).

When the two have gone, Rosina and Figaro enter. Figaro asks Rosina to write a few encouraging words to Lindoro, which she has actually already written. (Duet: "Dunque io son...tu non m'inganni?"; "Then I'm the one...you're not fooling me?"). Although surprised by Bartolo, Rosina manages to fool him, but he remains suspicious. (Aria: "A un dottor della mia sorte"; "To a doctor of my class").

Count Almaviva, disguised as a soldier and pretending to be drunk, enters the house and demands to be quartered there. In fear of the drunken man, Berta the housekeeper rushes to Bartolo for protection. Bartolo tells the "soldier" that he (Bartolo) has an official exemption which excuses him from the requirement to quarter soldiers in his home. Almaviva pretends to be too drunk and belligerent to understand, and dares Bartolo to brawl. While Bartolo searches his cluttered desk for the official document which would prove his exemption, Almaviva whispers to Rosina that he is Lindoro in disguise, and passes a love-letter to her. Bartolo suspiciously demands to know what is in the piece of paper in Rosina's hands, but she fools him by handing over her laundry list. Bartolo and the Count argue loudly. Basilio enters; then Figaro, who warns that the noise of the argument is rousing the whole neighborhood. Finally, the noise attracts the attention of the Officer of the Watch and his troops, who crowd into the room. Bartolo demands that the Officer arrest the "drunken soldier". The Officer starts to do so, but Almaviva quietly reveals his true identity to the Officer, and he (the Officer) backs off and stands down. Bartolo and Basilio are astonished and mystified; Figaro laughs quietly at them. (Finale: "Fredda ed immobile, come una statua"; "Cold and still, just like a statue"). The confusion intensifies and causes everyone to suffer headaches and auditory hallucinations ("Mi par d'esser con la testa in un'orrida fucina; dell'incudini sonore l'importuno strepitar."; "My head seems to be in a fiery forge: the sound of the anvils deafens the ear.")

Act 2
A room in Bartolo's house with a piano

Almaviva again appears at the doctor's house, this time disguised as a priest who is also a singing tutor and pretending to act as substitute for the supposedly ailing Basilio, Rosina's regular singing teacher. Initially, Bartolo is suspicious, but does allow Almaviva to enter when the Count gives him Rosina's letter. He describes his plan to discredit Lindoro whom he believes to be one of the Count's servants, intent on pursuing women for his master. While Almaviva pretends to give Rosina her singing lesson, Figaro arrives to shave Bartolo. Bartolo demurs, but Figaro makes such a scene he agrees, but in order not to leave the supposed music master alone with Rosina, the doctor has Figaro shave him right there in the music room. When Basilio suddenly appears, he is bribed by a full purse from Almaviva and persuaded to leave again, with much discussion of how ill he looks. (Quintet: "Don Basilio! – Cosa veggo!"; "Don Basilio! – What do I see?"). Figaro begins to shave Bartolo, but Bartolo overhears the lovers conspiring, and angrily drives everybody away.

The scene returns to the location of act 1 with a grill looking out onto the square. Bartolo orders Basilio to have the notary ready to marry him to Rosina that evening. He also explains his plot to come between the lovers. Basilio leaves and Rosina arrives. Bartolo shows Rosina the letter she wrote to "Lindoro", and persuades her that this is evidence that Lindoro is merely a flunky of Almaviva and is toying with her at Almaviva's behest. Rosina believes him and agrees to marry him.

During an instrumental interlude, the music creates a thunder storm to indicate the passage of time. The Count and Figaro climb up a ladder to the balcony and enter the room through a window. Rosina shows Almaviva the letter and accuses him of betraying her. Almaviva reveals his identity and the two reconcile. While Almaviva and Rosina are enraptured by one another, Figaro keeps urging them to leave. Two people are heard approaching the front door, who later turn out to be Basilio and the notary. However, when the Count, Rosina, and Figaro attempt to leave by way of the ladder, they discover it has been removed. The marriage contract requires two witnesses; Figaro is one, but another is needed. The Count makes Basilio an offer he can't refuse: the choice of accepting a bribe and being a witness to his marriage or receiving two bullets in the head (an easy choice, Basilio says). He and Figaro witness the signatures to a marriage contract between the Count and Rosina. Bartolo barges in, accompanied by the Officer and the men of the watch, but too late; the marriage is already complete. The befuddled Bartolo (who was the one who had removed the ladder) is pacified by being allowed to retain Rosina's dowry. The opera concludes with an anthem to love ("Amor e fede eterna, si vegga in noi regnar!").