Adina, a beautiful and wealthy landowner, is resting under the shade of a large tree on her estate with her workers. A young, poor peasant villager, Nemorino spies on Adina from a distance as she reads her workers the story of Tristan and Isolde. Nemorino wants nothing more than to be with Adina, but he is sad - because he is poor, he can only offer his love. Adina has been indifferent to him up to this point. As Adina reads the story to her workers, Nemorino convinces himself that he needs a love potion to win her heart - just like Tristan and Islode. After she finishes reading, Sergeant Belcore and his troops make their way to Adina.
Belcore flirts with Adina before finally proposing to her in front everyone. Adina casually and politely tells him that she will think it over. Adina and Nemorino are left alone when the troops and workers leave. Nemorino takes the opportunity to declare his love for her. Adina, still indifferent to his declarations, tells him that he has no time to love her. He has a sick uncle that he must take care of first.
Back in the town piazza, Dr. Dulcamara, a traveling salesman, arrives in grand fashion and presents his wares and elixirs to the townspeople. He claims to have a supply of cure-all potions, and after making a persuasive presentation, quickly sells many bottles to gullible villagers. The lovesick Nemorino asks Dulcamara if he possesses a love potion similar to Tristan and Isolde's. Dulcamara tells Nemorino that he, in fact, has a draught that will do the trick. He sells the love elixir to Nemorino for all the money Nemorino has in his pockets. Without hesitation, Nemorino gives Dulcamara all he has and downs the liquid within moments of acquiring it. Little does he know that the elixir was only wine. Before Nemorino becomes drunk, Dulcamara tells him the potion will take effect in one days time before he hastily makes an exit. Completely drunk, Nemorino approaches Adina when she enters. Confident his potion will work, he turns the table on Adina and treats her indifferently. Adina becomes angry at Nemorino's new attitude and decides to punish him by marrying Sgt. Belcore. Belcore tells her they must marry at once since he and his troops are scheduled to dispatch the following morning. Adina agrees, despite Nemorino's protests to wait one more day. She invites the townspeople to the eminent wedding. Panicked, Nemorino calls out for Dulcamara.
Outside, Adina and Dulcamara entertain the guests while waiting for the notary to officiate the wedding. Adina, upset that Nemorino has not yet appeared, has waited as long as she could and enters the chapel with the notary and the rest of the crowd to sign the marriage contract. Dulcamara remains behind to help himself to the refreshments. Nemorino shows up and begs Dulcamara for a love potion that will work instantly. Since Nemorino spent all his money on the first potion, Dulcamara refuses to help and goes inside. Sgt. Belcore makes his way outside wondering aloud why Adina has suddenly postponed the wedding by not signing the contract. After seeing a sulking Nemorino, Belcore approaches him to find out what is wrong. Nemorino explains that he has no money. Belcore seizes the opportunity to remove his rival from the picture, and tells him that if he signs up for the army, he'll immediately get a signing bonus. Nemorino agrees, secretly knowing that he'll take the money and run.
Later that evening, the women of the town gather to discuss Nemorino's sudden gain in wealth. His sick uncle has finally passed away, leaving him a great sum of money. When Nemorino appears, drunk again after buying another large "love potion" from Dulcamara, the women flock to his side. They flirt and coo over him leading him to think the potion is working. He has no idea his uncle has passed. Adina arrives and sees Nemorino acting differently than before. She asks Dulcamara about Nemorino and he tells her that the foolish boy has spent all his money and even joined the army in order to buy a love potion for some woman. Realizing that she is the woman, she regrets teasing and acting indifferently towards Nemorino. She realizes that his love for her is real and she too falls in love with him. She rejects Dulcamara's sales pitch of a potion of her own by telling him that she has her own means of gaining Nemorino's love. When she approaches him, he acts indifferently to her again. Adina rushes away leaving Nemorino alone. Nemorino thinks about the tear he has just seen on Adina's face and feels badly. He realizes that she must love him too. When she returns, she hands him his enlistment contract. She tells him that she has bought it and he is able to live freely. Finally, she confesses her love for him and they finally embrace. Sgt. Belcore arrives to see the two in each others arms. Adina apologizes to him, and Belcore takes the news very well. He proclaims there are plenty of women in the world from which to choose. Dulcamara spins a new sales pitch crediting Nemorino's happy ending to Dulcamara's love potion. Dulcamara sells dozens of bottles before leaving the small town.