Benjamin Franklin Pinkerton, a Lieutenant in the United States Navy, is inspecting his new house, built on a hillside overlooking Nagasaki harbor. The marriage broker Goro has arranged for the house and for Pinkerton’s marriage to the geisha Cio-Cio-San, who is also known as Madame Butterfly. Sharpless, the American consul, arrives for the ceremony and warns Pinkerton that Butterfly is taking the marriage very seriously; Pinkerton himself considers it something of a lark, although he is enchanted with Butterfly. She arrives with her friends and tells Pinkerton that she has renounced her religion for his sake. When Butterfly’s relatives arrive, the wedding ceremony begins, but it is interrupted by her uncle, the Bonze, who curses her for having abandoned her religion. The family members depart, leaving Butterfly alone with Pinkerton. As night descends, they sing of their love and slowly enter their new house.

Scene 1. Three years have passed. Pinkerton departed long ago and Suzuki, Butterfly’s maid, implores her to forget her American husband, but she refuses, having faith in his promise to return. Sharpless and Goro try to persuade Butterfly to marry the wealthy Prince Yamadori, without success. Sharpless starts to read a letter from Pinkerton, which suggests that he may never return, but Butterfly rejects the implication and shows Sharpless her son, Trouble, who was fathered by Pinkerton before his departure. The harbor cannon fires to announce the arrival of a foreign vessel, which Butterfly recognizes as the Abraham Lincoln, Pinkerton’s ship. She and Suzuki strew flowers throughout the house; she dons her wedding gown and, with Suzuki and Trouble, awaits the arrival of her husband as the sun begins to set.

Scene 2. Butterfly has maintained her vigil the entire night. As dawn breaks, Suzuki persuades her to rest. Sharpless and Pinkerton arrive, and Suzuki soon discovers that the woman with them is Pinkerton’s new wife, Kate. Sharpless tells Suzuki that they want to ensure a good American upbringing for Trouble and he then reproaches Pinkerton for his heartlessness. The latter bids an anguished farewell to the site of his past happiness and leaves, unable to face his Japanese bride. Butterfly enters and, after the situation is explained to her, agrees to give up the child if Pinkerton will return in 30 minutes. She bids a last farewell to her son, then takes up the dagger with which her father committed hara-kiri. She stabs herself, just as Pinkerton is arriving for his son.