A village in the Basque country. Nemorino has always loved Adina but does not dare declare himself. Adina reads aloud the story of Tristan and Isolde and the love potion. The charlatan Dulcamara arrives with his cart full of cures for everything. Nemorino asks for the love elixir. Dulcamara sells him a bottle of red wine, telling him it will work within twenty-four hours — but he will already be gone. Nemorino drinks and immediately feels invincible. His breezy new behaviour bewilders and irritates Adina, who out of spite agrees to marry the sergeant Belcore.

Nemorino, desperate, enlists in the army to get money for more potion. Meanwhile news spreads that his rich uncle has died leaving him his inheritance — news he himself does not yet know. All the village girls begin to court him. Nemorino does not understand: it must be the elixir working! Adina watches him, realises she truly loves him, buys out his army enlistment. Nemorino sees her shed a tear. He has his answer.