I. At a ball in his palace, the Duke sings of a life of pleasure with as many women as possible (Questa o quella - "This woman or that"). He has seen an unknown beauty in church and desires to possess her, but he also wishes to seduce the Countess of
Ceprano. Rigoletto, the Duke's hunchbacked court jester, mocks the husbands of the ladies to whom the Duke is paying attention, and advises the Duke to get rid of them by prison or death. Marullo informs the noblemen that Rigoletto has a "lover", and the noblemen cannot believe it. The noblemen resolve to take vengeance on
Rigoletto. Subsequently Rigoletto mocks Count Monterone, whose daughter the Duke had seduced. Count Monterone is arrested at the Duke's order and curses the Duke and
Rigoletto. The curse genuinely terrifies Rigoletto.
Thinking of the curse, Rigoletto approaches his house and is accosted by the assassin
Sparafucile, who offers his services. Rigoletto contemplates the similarities between the two of them
(Pari siamo! - "We are alike!"); Sparafucile kills men with his sword, and Rigoletto uses "a tongue of malice" to stab his victims. Rigoletto opens a door in the wall and returns home to his daughter
Gilda. They greet each other warmly (Figlia!" "Mio padre! - "Daughter!" "My father!"). Rigoletto has been concealing his daughter from the Duke and the rest of the city, and she does not know her father's occupation. Since he has forbidden her to appear in public, she has been nowhere except to church and does not even know her own father's name.
When Rigoletto has gone, the Duke appears and overhears Gilda confess to her nurse Giovanna that she feels guilty for not having told her father about a student she had met at the church, but that she would love him even more if he were poor. Just as she declares her love, the Duke enters, overjoyed.
Gilda, alarmed, calls for Giovanna, but the Duke has sent her away. He convinces Gilda of his love (E il sol dell'anima - "Love is the sunshine of the soul"), and she responds. When she asks for his name, he hesitantly calls himself Gualtier
Maldè. Hearing sounds and fearing that her father has returned, Gilda sends the Duke away after they quickly repeat their vows of love to each other
(Addio, addio - "Farewell, farewell"). Alone, Gilda meditates on her love for the student
(Gualtier Maldè! ... Caro nome - "Dearest name").
II. The Duke is concerned that Gilda has disappeared (Ella mi fu rapita! - "She was stolen from me!" and Parmi veder le lagrime - "I seem to see tears"). The noblemen then enter and inform him that they have captured Rigoletto's mistress. By their description, he recognizes it to be Gilda, and he rushes off to the room where she is held (Possente amor mi chiama - "Mighty love beckons me"). Pleased by the Duke's strange excitement, the courtiers now make sport with Rigoletto, who enters singing. He tries to find Gilda by pretending to be uncaring, as he fears she may fall into the hands of the Duke. Finally, he admits that he is in fact seeking his daughter and asks the courtiers to return her to him (Cortigiani, vil razza dannata - "Accursed race of courtiers"). The men beat up Rigoletto after his attempt to run into the room Gilda is being held in. Gilda rushes in and begs her father to send the people away. The men leave the room believing Rigoletto has gone mad. Gilda describes to her father what has happened to her in the palace (Tutte le feste al tempio - "On all the blessed days"). Rigoletto demands vengeance against the Duke, while Gilda pleads for him (Duet: Sì! Vendetta, tremenda vendetta! - "Yes! Revenge, terrible revenge!").
III. A portion of Sparafucile's house is seen, with two rooms open to the view of the audience. Rigoletto and Gilda, who still loves the Duke, arrive outside. The Duke's voice can be heard (La donna è mobile- "Woman is fickle") laying out the infidelity and fickle nature of women. Rigoletto makes Gilda realize that it is the Duke who is in the assassin's house and that he is attempting to seduce Sparafucile's sister, Maddalena.(Bella figlia dell'amore - "Sweet daughter of love")
Rigoletto bargains with the assassin, who is ready to murder his guest for money, and offers him 20 scudi for killing the Duke. He orders his daughter to put on a man's clothes in order to prepare to go to Verona and states that he plans to follow later. With falling darkness, a thunderstorm approaches and the Duke determines to remain in the house. Sparafucile assigns to him the ground floor sleeping quarters.
Gilda, who still loves the Duke despite knowing him to be unfaithful, returns dressed as a man. She overhears Maddalena begging for the Duke's life, and Sparafucile promises her that if by midnight another can be found in place of the Duke, he will spare the Duke's life. Gilda resolves to sacrifice herself for the Duke and enters the house. She is immediately mortally wounded and collapses.
At midnight, when Rigoletto arrives with money, he receives a corpse wrapped in a sack, and rejoices in his triumph. Weighting it with stones, he is about to cast the sack into the river when he hears the voice of the Duke singing a reprise of his "La donna è mobile" aria. Bewildered, Rigoletto opens the sack and, to his despair, discovers his mortally wounded daughter. For a moment, she revives and declares she is glad to die for her beloved (V'ho ingannato - "Father, I deceived you"). She dies in his arms. Rigoletto's wildest fear materializes when he cries out in horror: "The curse!"
Later, the hostile noblemen outside the walled garden (believing Gilda to be the jester's mistress) get ready to abduct the helpless girl. Convincing Rigoletto that they are actually abducting the Countess Ceprano, they blindfold him and use him to help with the abduction. He assists them, and Gilda is carried away by the noblemen. Upon realizing that it was in fact Gilda who was carried away, Rigoletto collapses, remembering the curse.