Giannetta and a group of farmhands are finishing their morning harvesting. Nemorino watches Adina from a distance, sad about being too poor to offer her anything but his love and too shy to approach her. Adina reads the story of Tristan and Isolde and how Tristan won Isolde’s affection with a love potion. Sergeant Belcore arrives with his regiment of soldiers. He flirts with the girls and then declares his passion for Adina, asking her to marry him. She is flattered but refuses the offer. The farmhands return to work, and Nemorino finds the courage to declare his love for Adina. She laughs at him, telling him she is too capricious to settle down. Dr. Dulcamara arrives with a supply of patent medicine for sale. Nemorino asks him if he knows of the magic elixir of love with which Tristan won Isolde. Dulcamara replies that it was he who created it and he sells a bottle of it to Nemorino. The lad drinks it at once, not realizing that it is simply Bordeaux wine, and the effect of the alcohol is immediate. Certain that he will win Adina’s love, Nemorino begins to treat her indifferently. To get even, Adina begins to flirt with Belcore and finally agrees to marry him. When orders arrive calling for Belcore to report to duty at once, he and Adina decide to wed that very evening.

Annoyed because Nemorino has not attended the party preceding her marriage, Adina delays signing the marriage contract. Nemorino enters and asks the doctor’s help. He says Nemorino must double the amount of potion and gives him another bottle of wine. In order to obtain the money to pay for the elixir, Nemorino joins Belcore’s regiment and receives an enlistment bonus. The village girls learn that Nemorino’s rich uncle has died, leaving the lad a large inheritance. Nemorino staggers in, reeling from the double dose of elixir. The girls crowd around him, which Nemorino, unaware of his inheritance, credits to Dulcamara’s potion. Adina sees Nemorino with the girls and becomes jealous. She is now determined to win him for herself. Nemorino returns, sad at the thought of leaving his village and Adina for the army. Adina joins him and tells him that she has bought back his enlistment papers so that they can be married. All join in praising Dulcamara and his magic elixir.