Act I
Violetta's house in Paris, August 1847
Violetta throws a party attended by her "protector," Baron Douphol and her friends, including Flora, a fellow courtesan. Gastone introduces Violetta to Alfredo Germont, a young man who admits that he is one of her greatest admirers. Violetta welcomes Alfredo to her gathering. Gastone invites Alfredo to offer a drinking song, and Alfredo sings the praises of wine and the love it inspires. Violetta joins him, urging everyone to enjoy the fleeting pleasures of love and life. As the guests move into the ballroom, Violetta has a sudden attack of faintness, an unwelcome reminder of her declining health. Alfredo urges her to abandon her exhausting way of life, and tells her that he has loved her since he first saw her. Violetta tactfully suggests that she is not the kind of woman he should fall deeply in love with; nonetheless, she invites Alfredo to visit her again. When her guests have left, Violetta muses over his declarations of love. Disturbed to discover that her own emotions have been deeply stirred, she resolves to forget Alfredo and devote herself to the shallow pleasures of the courtesan's world.

Act II
A country house near Paris, November 1847
Alfredo has been living for three months with Violetta in her country house. He is ashamed to discover that she has been secretly selling her possessions to meet their expenses.

Alone, Violetta receives a letter from Flora, inviting her to a party in Paris. An unexpected visitor arrives: Giorgio Germont, Alfredo's father. Germont asks her for a great sacrifice; his daughter's marriage prospects have been threatened by Alfredo's scandalous association with Violetta. Germont convinces her that leaving Alfredo would be the most generous, selfless thing she could do for him. Violetta knows that because she is mortally ill, any future happiness is unlikely with Alfredo. She writes two letters: the first is an acceptance of Flora's invitation; the second is addressed to Alfredo.

When Alfredo returns, Violetta attempts to hide her great agitation. Desperately assuring him of her love, she goes off in a carriage to Paris. Alone, Alfredo reads Violetta's letter, which informs him that she is returning to Baron Douphol. Germont returns to console his son. Alfredo sees Flora's invitation and, unaware of Violetta's sacrifice, vows to avenge himself for her apparent faithlessness at Flora's party.

That evening, Flora's guests are entertained by masqueraders dressed as gypsies and matadors. Alfredo arrives, alone; Violetta enters shortly afterward with Baron Douphol. Alfredo goes to the card table, where he is soon joined by the Baron, but Alfredo's good luck at gambling is unmatched. When the guests sit down to supper, Violetta privately begs Alfredo to leave. Furious, he insults her in front of everyone, throwing his winnings at her as "payment" for their time together. The elder Germont comes in, joining the assembled crowd in expressing their outrage.

Act III
Violetta's room, February 1848
Violetta is near death, alone and impoverished. Germont has written to tell her that Alfredo, who had fled abroad after wounding Baron Douphol in a duel, has been told of Violetta's sacrifice and is on his way back to Paris. When he returns, the lovers are reunited with tender words. Giorgio Germont also arrives, filled with remorse, but there is nothing to be done. Violetta feels a sudden rush of exhilaration as her pain disappears, and she dies.