The opera begins in 1904, and at a Nagasaki house that B. F. Pinkerton, a Navy Lieutenant, recently purchased. A marriage broker named Goro shows Pinkerton around the house, and Pinkerton is fascinated by the sliding screen walls. Throughout their discussion, they compare the house to the marriage contract.

Goro introduces Pinkerton to his household servants. Suzuki, the servant for Pinkerton’s fiancée, Butterfly, compliments Pinkerton’s smile, but Pinkerton is bored by her, so Goro cuts her off and sends all the servants away. Goro and Pinkerton discuss the day’s wedding plans: Pinkerton will meet Butterfly’s family and sign the marriage contract while witnessed by the Registrar and Consul. As Goro describes Butterfly’s family, the US Consul, Sharpless, arrives. He comments on the high elevation of the house, and Pinkerton sends Goro to get them refreshments.

In the garden, Pinkerton and Sharpless discuss the view of the sea and the delicacy of the paper screens in the house. Again, the marriage contract is compared to the housing contract—both are for 999 years, but each can be canceled monthly. Then, Pinkerton explains that he wants the “fairest Pearl of every country” (72) while traveling with the US Navy.