A festive ball is taking place at the court of Mantua. The Duke happily tells the courtier Borsa about his amorous adventure with a beautiful girl who lives at a house in a remote alley where she is visited by an unknown man every evening. He has met her only in church so far, so she does not know who he is. The Duke makes advances to Countess Ceprano, and her husband is mocked by Rigoletto, the hunchbacked jester. Marullo reveals a sensation to other courtiers: he has discovered that Rigoletto has a mistress. All arcs convulsed with laughter. Rigoletto suggests ways in which the Duke might get rid of the Count in order to seduce his wife. Ceprano is enraged. Suddenly Monterone storms in, accusing the Duke of having dishonoured his daughter. When the jester mocks his grief the old man curses him. Rigoletto is filled with a sense of dread.
Rigoletto remembers Monterone's curse with dark foreboding. Sparafucile the hired assassin approaches him and offers his services. Left alone, Rigoletto reflects on the humiliations of his existence as a cripple and as court buffoon. Only in his love for his daughter Gilda is he a human being. Gilda comes out of the house and throws herself into his arms. When she begs him to tell her about her early life, Rigoletto pours out the sorrow of his lost Love; his daughter is the only joy remaining to him, He forbids Gilda ought to leave the house, and orders the housekeeper Giovanna to guard her. Having bribed Giovanna to admit him, the Duke - incognito - surprizes Gilda and makes passionate declarations of love. Gilda is overjoyed. In the darkness Ceprano, Marullo and the courtiers arrive, intending to abduct Rigoletto's supposed mistress. Made to believe that it is Countess Ceprano, who is being abducted, the blindfolded Rigoletto even holds the ladder for them. As Gilda is dragged away he tears the blindfold from his eyes, too late. The curse has begun to take effect.
The Duke has discovered to his genuine despair that Gilda has been abducted. The courtiers triumphantly tell how they seized Rigoletto's 'mistress' - Gilda. The Duke rushes to her. Rigoletto appears with feigned indifference. He has to realize that Gilda is with the Duke. The courtiers prevent him from rushing in. When she is brought to him, Gilda tearfully confesses her liaison with the Duke, which has robbed her of her honour. Led past on his way to prison, Monterone again curses the despairing Rigoletto, who thinks only of vengeance.
Rigoletto has paid Sparafucile to murder the Dulce. He and Gilda watch the building from a vantagepoint outside. Gilda recognizes the Duke flirting with the assassin's sister Maddalena. Taking pity on the handsome young woman, Maddalena persuades her brother to kill someone else instead of him. Gilda overhears the plan and resolves to sacrifice herself for her lover. She knocks at the door behind which Sparafucile is lurking with a knife ready to slay whoever enters. The door opens - night and the thunderstorm obscure everything. The victim is concealed in a sack. The returning Rigoletto is about to throw it into the river when he hears the Duke singing his wooing canzone. Rigoletto tears open the sack to discover his dying daughter. She begs his forgiveness, and dies in the hope of heavenly bliss. Rigoletto is utterly broken. Monterone's curse has been fulfilled.