SCENE 1: Don Pasquale's house
Elderly bachelor Don Pasquale is planning to marry, to spite his nephew Ernesto who is refusing to marry the girl of his uncle's choice. Dr Malatesta, who has been commissoned to find the bride, tells him that his sister Sofronia, fresh from the convent, innocent, shy and modest, will suit his friend exactly, provoking a frenzy of anticipation in Don Pasquale.
He asks Ernesto for the last time if he will agree to the chosen bride; and when he refuses - being in love with the young and attractive, but not rich, widow Norina - his uncle orders him to leave the house, as he is about to get married himself.
Ernesto advises caution and suggests consulting Dr Malatesta, whose good sense and friendship he trusts, only to learn that the doctor has actually offered his own sister as the bride. Ernesto feels betrayed.
SCENE 2: Norina's house
Norina, reading about the power of a lady's glance to bring her chosen knight to her feet, prides herself on having the same ability - only she has a good heart and does not abuse her power. She is waiting for Dr Malatesta, who has indicated that he has a plan to help her and Ernesto, but not revealed the details. She receives a note from Ernesto which she hands to the doctor when he arrives - Ernesto, accusing his friend of treachery and of having duped Don Pasquale into marrying his sister, announces that, disinherited by his uncle, he is leaving both home and country.
Dr Malatesta reassures Norina and explains his plan. She is to go through a mock marriage ceremony with Don Pasquale (he has a cousin who will pretend to be the notary), pretending to be a shy convent-bred girl; and then to change into a virago after the ceremony. Satisfied that this plan will help Ernesto, she is ready to throw herself into the play-acting.
Don Pasquale's house
Ernesto sadly prepares to leave for foreign parts. Dr Malatesta brings the heavily veiled Norina, who pretends to be frightened of Don Pasquale and alarmed at the idea of taking off her veil in front of a man. Questioning her about her interests, Don Pasquale is charmed when she answers that she does not care for the theatre or going out, but prefers to sit at home and sew. His delight increases when she finally takes off the veil.
The marriage contract is signed. Ernesto's voice is heard outside, arguing with the servants who refuse to let him in, but he is allowed in when the "notary" explains the need for another witness. He is thunderstuck at the sight of Norina, but the doctor manages to draw him aside and persuade him to do nothing rash, assuring him that everything is under control.
When Don Pasquale wants to kiss his bride she refuses. What's more, she says, he is too old for her to be seen out with. She needs a young escort -Ernesto, for instance - and threatens to hit Don Pasquale if he crosses her. Summoning the servants, she declares that there are not enough of them, and instructs the major-domo to engage more and to order her a coach and horses and to send for hairdressers, dressmakers and jewellers. She also plans to refurnish the old-fashioned house.
She takes advantage of the ensuing confusion, while Don Pasquale expostulates and Dr Malatesta pretends to be shocked, to reassure Ernesto, who by now has a fair idea what is going on and rejoices in his uncle's discomfiture.
SCENE 1: Don Pasquale's house
Servants rush around, carrying out Norina's commands, while Don Pasquale tears his hair at the mounting pile of bills. When Norina appears, all dressed up and ready to go to the theatre, he tries to stop her, accusing her of being a flirt, and she slaps his face. Although she regrets having had to take such a step, she believes it is necessary to drive the point home; and in fact it produces immediate results, as Don Pasquale starts demanding a divorce. Norina flounces out, deliberately dropping a paper. Picking it up, expecting yet another bill, Don Pasquale finds it is an unsigned assignation for that evening in the garden.
He sends for Malatesta, who first arranges further details of the plot with Ernesto, who is to meet Norina in the garden, but slip away before he can be discovered. Then he attends to Don Pasquale's complaints about the treatment he has received and about the letter. He and Malatesta plan to catch Norina and her mysterious lover in the garden.
SCENE 2: Don Pasquale's garden
Ernesto serenades Norina, who then joins him in a love duet. Ernesto then slips away before Don Pasquale and Dr Malatesta can catch him. Don Pasquale again announces his intention of divorcing his wife and the doctor suggests that she will be more likely to agree and leave the house if another bride comes into it - Ernesto's Norina. Norina pretends to object, thus spurring Don Pasquale to approve of Ernesto's marriage. At Malatesta's urging, he also promises to give Ernesto a handsome allowance. Ernesto then appears and Norina's true identity is revealed. Don Pasquale's anger at the deception gives way to his relief that he is not, after all, really married to a spendthrift, unfaithful shrew, and he readily gives his blessing to the young couple.