The play takes place in the Spanish castle of Aguas Frescas, home of the Count Almaviva, the Governor of Andalusia, and his wife, the Countess Rosine. The nearest familiar city is Seville, capital of the Andalusia region. It opens in one of the castle bedrooms which is being prepared for Figaro and Suzanne, who will spend their wedding night there. Suzanne is not enamored of the room because she thinks the only reason the Count offered them this room in particular is that his bedroom is next door and this gives him closer proximity to try to pursue her to begin an affair with him. The Count has long had a reputation as a philanderer and inveterate pursuer of women and this reputation is entirely justified. Figaro is anxious to solve the problem and ease her worries.
Enter Dr Bartholo and his housekeeper, Marceline. They are visiting to discuss a lawsuit they are filing against Figaro whom they claim owes Marceline money; he had promised to marry her if he did not repay this debt. His marriage to Suzanne has the potential to make the contract null and void, hence the talk of a lawsuit. Dr Bartholo is almost rubbing his hands with glee when he learns that Rosine is unhappily married (after all, he had wanted to marry her himself).
There is a short confrontation between Suzanne and Marceline, who is in love with Figaro herself and hoping to dissuade Suzanne from marrying him. Their heated words are interrupted by a page boy named Cherubin who is the Count's personal page and the Countess's godson, and who falls in love with every woman he meets. He has been fired because he was found in Fanchette's bedroom; Fanchette has many boyfriends and is the castle gardener's daughter and also Suzanne's cousin. This discussion takes place mostly after Marceline has departed, and when Suzanne hears the Count approaching she urges Cherubin to hide since she doesn't particularly want them to be discovered together in a bedroom either. He hides behind an armchair and because of this witnesses the Count propositioning Suzanne, who continues to spurn his advances. Bazile then comes into the room and hearing him, the Count, who also does not want to be caught in a bedroom with someone else's fiance, hides behind the armchair, forcing Cherubin to leap on top of the armchair so that the Count will not realize that he was hiding there all along. Suzanne deftly throws a dress over him so that he will not be seen by Bazile either. Bazile loiters at his leisure in the doorway of the bedroom and proceeds to share all of the gossip of the day. Most is harmless and but when he tells her that there is a rumor that Cherubin and the Countess are having an affair the Count cannot contain himself and leaps angrily from behind the armchair. Suzanne is horrified because now that Bazile has seen the Count, and taken on board the fact he was hiding, he will think that there is something going on between them. The Count dramatically re-creates what happened when he found Cherubin hiding in Fanchette's room by removing the dress from the armchair with a flourish, revealing the page for the second time. However, the Count is now concerned that the page knows too much about his pressuring Suzanne into a relationship and decides the only thing to do is to promote him in to the military and send him away.
Figaro, the Countess and a group of wedding guests join them then, wanting to begin the ceremony immediately, but the Count manages to persuade them to wait a little while longer.
Act Two begins in the Countess's bedroom after Suzanne has told her about the Count's constant attentions. Figaro has a plan to divert the Count; he will tell him of a rumor that Rosine is having an affair and that she has invited her secret lover to the wedding. He believes this will intrigue the Count and that he will be eager for the wedding to proceed so that he can see the lover for himself. The women don't think it is a very good plot because they don't think that it will work so Figaro comes up with something more elaborate. He will tell the Count that Suzanne has decided to accept his advances but will embarass the Count by sending Cherubin to him dressed in Suzanne's gown. They begin to dress the page but just as Suzanne is leaving, the Count comes in and so Cherubin hides in the dressing room leaving the Count growing more and more suspicious that something is going on behind his back. Cherubin flees out of the dressing room window and Suzanne takes his place there so that when the Count breaks open the door, it appears that she was there all along. This calms him down, at least until the gardener appears shouting about a half-naked young man jumping from the Countess's window. As the Count grows angry again Figaro decides to admit to being the "jumper", telling the Count he started the rumor of the Countess's affair as a prank but on thinking about it, whilst he was waiting for Suzanne, he became nervous about the Count's reaction and fled the room.
Marceline, the doctor and the judge arrive then; it's time for Figaro's trial to start and Act Three revolves around this side plot. At the behest of Rosine, Suzanne tells the Count that she will begin an affair with him and asks him to meet her after her wedding. Rather than disguise the page as Suzanne, Rosine has decided to appear to her husband herself. The Count is angered when he overhears Suzanne telling Figaro that she hopes this will enable them to win the case. As Figaro is tried, the Court seem preoccupied with the fact he has no name other than "Figaro" - no last name at all. He explains that he was kidnapped as a baby and therefore does not know what his real last name is. That's why he goes by "Figaro". The Court inexplicably rules in Marceline's favor, thereby forcing Figaro to marry her. Marceline recognizes a mark in the shape of a lobster on Figaro's arm and realizes that he is her son and that Dr Bartholo is his father. Suzanne then enters with enough money to pay Marceline what Figaro owes her, having been given funds by Rosine. This is the final straw for the Count who is not getting his own way about anything at all and storms out of the room.
Figaro is overjoyed to have found his long lost parents, but Suzanne's uncle now forbids her to marry him because his is illegitimate. To solve this new issue, Marceline and the doctor get married themselves.
At the start of Act Four, Figaro tells Suzanne that the Count still thinks she is going to meet him in the garden after her wedding. They write him a note that is a song, which is a throwback reference to the previous "Barber of Seville" when the Count would communicate with Rosine on sheet music. In the note Suzanne promises to meet him underneath the chestnut tree in the garden. Everything becomes suddenly very confusing.
Fanchette enters the room with Cherubin who is disguised as a girl, and is accompanied by some girls from the village who have brought her flowers. Suzanne thanks him with a little kiss to the forehead. Antonio is aware that the page is in disguise, so when he enters with the Count, Rosine admits that she hid Cherubin in her bedroom earlier and the Count readies a punishment. Fanchette suddenly announces that she and the Count have been having an affair. Since he has promised he will give her whatever her heart desires, he must let her and Cherubin marry, and withhold punishment. The wedding is interrupted again by Bazile who had wanted to marry Marceline, but is horrified by the news that she is Figaro's mother and immediately changes his mind.
Fanchette tells Figaro that she is worried because she has lost the pin that the Count gave her to give back to Suzanne, that the letter had been sealed with. Figaro thinks that Suzanne really did decide to have an affair with the Count and vows revenge on them both.
He calls together a group of men at the start of Act Five, and orders them to walk in on Suzanne and the Count and to catch them in their affair. This would both humiliate them and also ensure he got a divorce. Figaro hides whilst the Countess and Suzanne enter, dressed in each other's clothing. They realize Figaro is watching which upsets Suzanne whose feelings are hurt by his lack of trust in her. The Count arrives and the disguised Countess goes off with him. Figaro is furious and complains woman he believes to be Rosine but then realizes it is his own wife who has remained true to both him, and to their original plan. He apologizes for his lack of trust in her and they make up quickly. When the Count sees whom he believes to be Rosine kissing Figaro he tries to stop their embrace. The real Countess then reveals herself and the Count begs forgiveness which she grants him.