Place: A 19th-century Sicilian village
Time: Easter morning

Before the action takes place, the young villager Turiddu had returned from military service to find that his fiancée Lola had married the carter Alfio while Turiddu was away. In revenge, Turiddu had seduced Santuzza, a young woman in the village. As the opera begins, Lola, overcome by her jealousy of Santuzza, has begun an adulterous affair with Turiddu.

The main square of the village

Offstage, Turiddu is heard singing a siciliana, "O Lola c'hai di latti la cammisa" ("O Lola! like the snow, pure in thy whiteness!"). To one side is the church; to the other is Lucia's wine shop and the house where she lives with her son, Turiddu. The villagers move about the square, singing of the beautiful spring day, "Gli aranci olezzano sui verdi margini" ("The air is sweet with orange blossoms") and a hymn to the Blessed Virgin Mary. Some villagers enter the church, and others wander off still singing.

Santuzza, having slept with Turiddu and suspecting that he has betrayed her for Lola, is distraught and approaches Lucia as she comes out of her house. Santuzza asks for Turiddu, but Lucia replies that he has gone to another town to fetch some wine. Santuzza tells her that he was seen during the night in the village. Lucia asks her inside to talk, but just at that moment Alfio arrives on his wagon, accompanied by the villagers. He praises the joys of a teamster's life and the beauty of Lola his bride. Alfio asks Lucia for some of her fine old wine. She tells him it has run out and Turiddu has gone away to buy more. Alfio replies that he had seen Turiddu early that morning near his cottage. Lucia starts to express surprise, but Santuzza stops her.

Alfio leaves. The choir inside the church is heard singing the Regina Coeli. Outside, the villagers sing an Easter Hymn, "Inneggiamo, il Signor non è morto" ("We rejoice that our Saviour is living!") joined by Santuzza. The villagers enter the church, while Santuzza and Lucia remain outside. Lucia asks Santuzza why she signalled her to remain silent when Alfio said that he had seen Turiddu that morning. Santuzza exclaims, "Voi lo sapete" ("You well know") and tells Lucia the story of her seduction by Turiddu and his affair with Lola. Lucia pities Santuzza, who feels dishonored, having been seduced by Turiddu only to be abandoned by him for his old flame, Lola. Santuzza feels she cannot enter the church, but begs Lucia to go inside herself and pray for Santuzza who stays behind to try to plead with Turiddu to leave Lola and return to her.

Turiddu arrives. Santuzza upbraids him for pretending to have gone away, when he was actually seeing Lola. Lola enters the square singing. She mocks Santuzza and goes inside the church. Turiddu turns to follow Lola, but Santuzza begs him to stay. Turiddu pushes her away. She clings to him. He loosens her hands, throws her to the ground, and enters the church. Alfio arrives looking for Lola. Santuzza tells him that his wife has betrayed him with Turiddu. Alfio swears to take vendetta (revenge) which causes Santuzza to repent for having disclosed the affair and begs Alfio to stop to no avail.

The square is empty as the orchestra plays the famous Intermezzo.

The villagers come out of the church. Turiddu is in high spirits because he is with Lola and Santuzza appears to have gone. He invites his friends to his mother’s wine shop where he sings a drinking song, "Viva, il vino spumeggiante" ("Hail to the bubbling wine!"). Alfio joins them. Turiddu offers him wine, but he refuses it. All understand that trouble is in the air. The women leave, taking Lola with them. In a brief exchange of words, Alfio challenges Turiddu to a duel. Following Sicilian custom, the two men embrace, and Turiddu, in a token of acceptance, bites Alfio’s ear, drawing blood which signifies a fight to the death. Alfio leaves and Turiddu calls Lucia back. He tells her that he is going outside to get some air and asks that she be a kindly mother to Santuzza if he should not return: "Un bacio, mamma! Un altro bacio!—Addio!" ("One kiss, mother! One more kiss! – Farewell!").

Turiddu rushes out. Lucia, weeping, wanders aimlessly around outside her house. Santuzza approaches and throws her arms around her. The villagers start to crowd around. Voices are heard in the distance and a woman cries, "They have murdered Turiddu!" Santuzza faints and Lucia collapses in the arms of the women villagers.

Place: Florence
Time: 1299

As Buoso Donati lies dead in his curtained four-poster bed, his relatives gather round to mourn his passing, but are really more interested in learning the contents of his will. Among those present are his cousins Zita and Simone, his poor-relation brother-in-law Betto, and Zita's nephew Rinuccio. Betto mentions a rumour he has heard that Buoso has left everything to a monastery; this disturbs the others and precipitates a frantic search for the will. The document is found by Rinuccio, who is confident that his uncle has left him plenty of money. He withholds the will momentarily and asks Zita to allow him to marry Lauretta, daughter of Gianni Schicchi, a newcomer to Florence. Zita replies that if Buoso has left them rich, he can marry whom he pleases; she and the other relatives are anxious to begin reading the will. A happy Rinuccio sends little Gherardino to fetch Schicchi and Lauretta.

As they read, the relatives' worst fears are soon realised; Buoso has indeed bequeathed his fortune to the monastery. They break out in woe and indignation and turn to Simone, the oldest present and a former mayor of Fucecchio, but he can offer no help. Rinuccio suggests that only Gianni Schicchi can advise them what to do, but this is scorned by Zita and the rest, who sneer at Schicchi's humble origins and now say that marriage to the daughter of such a peasant is out of the question. Rinuccio defends Schicchi in an aria "Avete torto" (You're mistaken), after which Schicchi and Lauretta arrive. Schicchi quickly grasps the situation, and Rinuccio begs him for help, but Schicchi is rudely told by Zita to "be off" and take his daughter with him. Rinuccio and Lauretta listen in despair as Schicchi announces that he will have nothing to do with such people. Lauretta makes a final plea to him with "O mio babbino caro" (Oh, my dear papa), and he agrees to look at the will. After twice scrutinizing it and concluding that nothing can be done, an idea occurs to him. He sends his daughter outside so that she will be innocent of what is to follow.

First, Schicchi establishes that no one other than those present knows that Buoso is dead. He then orders the body removed to another room. A knock announces the arrival of the doctor, Spinelloccio. Schicchi conceals himself behind the bed curtains, mimics Buoso's voice and declares that he's feeling better; he asks the doctor to return that evening. Boasting that he has never lost a patient, Spinelloccio departs. Schicchi then unveils his plan in the aria "Si corre dal notaio" (Run to the notary); having established in the doctor's mind that Buoso is still alive, Schicchi will disguise himself as Buoso and dictate a new will. All are delighted with the scheme, and importune Schicchi with personal requests for Buoso's various possessions, the most treasured of which are "the mule, the house and the mills at Signa". A funeral bell rings, and everyone fears that the news of Buoso's death has emerged, but it turns out that the bell is tolling for the death of a neighbour's Moorish servant. The relatives agree to leave the disposition of the mule, the house and the mills to Schicchi, though each in turn offers him a bribe. The women help him to change into Buoso's clothes as they sing the lyrical trio "Spogliati, bambolino" (Undress, little boy). Before taking his place in the bed, Schicchi warns the company of the grave punishment for those found to have falsified a will: exile from Florence together with the loss of a hand.

The notary arrives, and Schicchi starts to dictate the new will, declaring any prior will null and void. To general satisfaction he allocates the minor bequests, but when it comes to the mule, the house and the mills, he orders that these be left to "my devoted friend Gianni Schicchi". Incredulous, the family can do nothing while the lawyer is present, especially when Schicchi slyly reminds them of the penalties that discovery of the ruse will bring. Their outrage when the notary leaves is accompanied by a frenzy of looting as Schicchi chases them out of what is now his house.

Meanwhile, Lauretta and Rinuccio are rapt in a love duet, "Lauretta mia" - there is no bar to their marriage since Schicchi can provide a respectable dowry. Schicchi, returning, stands moved at the sight of the two lovers. He turns to the audience and asks them to agree that no better use could be found for Buoso's wealth: although the poet Dante has condemned him to hell for this trick, Schicchi asks the audience to forgive him in light of "extenuating circumstances."