On Catfish Row in Charleston, South Carolina, Jasbo Brown is playing the blues for a group of dancers. Clara sings a lullaby to her child (“Summertime”). The drug dealer Sporting Life, Clara’s husband Jake, and some of the other men are playing craps. Jake sings his child a lullaby of his own (“A woman is a sometime thing”). The beggar Porgy comes in to join the game; he defends Crown’s woman, Bess, who the others are talking about. When Jake accuses him of being soft on her, Porgy says that he isn’t soft on any woman; God made him a cripple and meant him to be lonely.
Crown enters with Bess. He’s drunk, and when he loses he starts a fight and kills Robbins with a cotton hook. Crown runs to hide, but tells Bess he’ll be back. Sporting Life offers to take her to New York with him, but she refuses. Nobody else will give her shelter when the police arrive except Porgy.
Porgy and Bess are at Robbins’ funeral, where Serena is leading the mourners. The police enter and arrest Peter as a “material witness.” Serena is still mourning (“My man’s gone now”) as she convinces the undertaker to bury Robbins for less than his usual fee, but as the scene ends, Bess leads the mourners in a spiritual. (“Oh, the train is at the station”).
A few weeks later, Jake and the Fishermen are working on their nets when Porgy leans out the window and compares his life to theirs. (“I got plenty o’ nuttin'”). Maria, a shopkeeper, chases Sportin’ Life away from her shop when he tries to sell his ‘happy dust’ near her store (“I hates yo’ struttin’ style”). Lawyer Frazier comes in and sells Bess a divorce for a dollar; when he learns that she and Crown were never married, he raises his fee to a dollar and a half. Mr. Archdale, a well-meaning white man, comes in and offers to pay Peter’s bail. The group is frightened by a low-flying buzzard. Porgy chases it away, saying that trouble is far away from him now (“Boss, dat bird mean trouble”).
All leave except Bess and Sporting Life, who asks her again to come to New York with him and tries to give her more dope, which she refuses. Porgy chases him away and he and Bess sing about their new happiness. (“Bess, you is my woman now”). All except Porgy leave for the church picnic.
At the picnic, Sporting Life sings about his own brand of religion (“It ain’t necessarily so”). All are getting ready to leave when Crown, hidden in the bushes, calls out to Bess. She tells him she’s Porgy’s woman now, but he won’t let her go. (“What you want wid Bess?”). He pushes her off into the thicket as the boat leaves without her.
Some time later, the fishermen are getting ready to leave as Bess raves, still delirious after Crown’s attack. Peter wants to send her to the hospital, but Serena would rather pray over her. The street fills with vendors, and eventually Bess emerges, and explains to Porgy that she wants to stay with him but that when Crown comes she’ll have to go with him. Porgy tells her that she doesn’t have to go with him (“I loves you, Porgy”). A hurricane begins to rise, and Clara, frightened for her husband, calls out his name.
Everyone, gathered in Clara’s room, prays for shelter from the storm. There is a knock at the door; Crown enters and tries to take Bess away; he laughs at the frightened townspeople and sings a bawdy song to counteract their prayers (“A red-headed woman”). Clara sees Jake’s boat and runs out to find him. Bess calls for a man to go after her; Crown goes, after taunting Porgy and asking him why he won’t go.
After the storm, the women are crying for their men; Sporting Life teases them and Bess. Crown enters; he and Porgy fight, and Porgy kills him.
The police and the coroner come to Catfish Row the next morning; they want to take Porgy down to identify Crown’s body. Sportin’ Life tells him that when he looks at him Crown’t wound will begin to bleed. Telling Bess that Porgy will be locked up for sure, Sportin’ Life forces some dope on her, and leaves more outside her door as he leaves.
Porgy returns; while he tries to distribute the gifts he bought with the money he made playing craps in jail, he discovers Bess is gone (“Oh, Bess, oh where’s my Bess”). He learns that she has gone off with Sportin’ Life to New York; he gets in his goat-cart and prepares to follow her as the curtain falls.