Fall in Paris. Violetta Valéry, a beautiful and engaging courtesan, is holding a supper party for her patron and lover, the Baron Douphol. Gaston introduces his friend, Alfredo Germont to her. He explains that Alfredo came every day during her recent illness to inquire about her health. It is clear that Violetta has been ill, but her friends do not realize she has the scourge of the 19th century, tuberculosis. In the famous Brindisi, or drinking song, Alfredo sings a toast to love, to which she replies. As the guests go off to dance, Violetta collapses in a fit of coughing. Quickly recovering, she tells them to proceed to the ballroom, but Alfredo lingers behind and declares his love for her. She laughs at his ardor, but is touched by his sincerity. She dismisses him, but tells him that he may return when the camellia she has given him has faded. The guests leave and she remains alone to consider Alfredo's invitation to love. She realizes that the social conventions that bind her life make true love impossible, and she resolves to continue her life of feverish gaiety in the thrilling aria Sempre Libera (Always Free) .
Violetta's country house in the spring. For several months Violetta has been living happily with Alfredo. Alfredo tells us that his soul is in heaven when he is with Violetta. He surprises the maid who has just returned from Paris. She reluctantly tells him that Violetta has been selling off her property to pay for the life she is now leading. His pride wounded, Alfredo leaves for Paris immediately to stop this. In his absence, Violetta receives a visit from his father, Giorgio Germont, a well-to-do businessman from the provinces who has come to confront the courtesan he believes is ruining his son's life. He tells her that their illicit love affair is the reason why his daughter cannot be married. At first, Violetta assumes Germont wants her to leave Alfredo until the wedding is over. But that is not what the old man wants. He reminds her that her past will always haunt them, and that true love can never be hers. In despair, Violetta tells him that Alfredo is all she lives for, and such a sacrifice would kill her. This is not simply melodrama. For in the months she has been in the country with Alfredo, her health has improved substantially and she truly believes she has escaped her past, and her illness. Giorgio cruelly tells her that someday her beauty will fade and Alfredo, like all men, will grow tired of her. Succumbing to his unrelenting demands, Violetta sacrifices herself to Germont's wishes, asking only to be embraced as a daughter and to allow her to break the news to Alfredo. Germont leaves Violetta to decide how to break it off with Alfredo. She wants to write him a letter and leave before he returns. Just then, Alfredo surprises her. Having finished her letter to him, she says she is leaving for a short while, but will return. Alfredo reads the letter and is crushed beyond belief. His father reappears to offer consolation and to ask him to come home to the family that loves him. Angrily rejecting this suggestion, Alfredo notices an invitation for that evening from Flora, one of Violetta's friends, and he concludes that this is where he will find her.
At Flora's, a magnificent party is underway complete with gambling, dancing, entertainment and gypsy fortunetellers. Violetta has returned to her former lover, Baron Douphol, and arrives with him. Alfredo then enters, to the surprise of everyone. He gambles with the Baron and wins a substantial sum. Violetta begs Alfredo to leave, but he forces her to explain her behavior; in desperation, and to protect Alfredo's father, she says that she no longer loves him. At this, Alfredo calls the guests to witness that he pays his debts in full and throws his winnings at the face of the courtesan. Flora's guests are outraged at his cruel behavior and the Baron challenges Alfredo to a duel.
Violetta's bedroom. It is winter, cold and desolate. Violetta's health has declined, the Baron has left her, and her money is almost spent. She tells Annina to give half of what little remains to the poor. She has received a letter from Alfredo's father explaining that Alfredo had wounded the Baron in a duel and that Alfredo has left Paris. He tells her that his son now knows the truth of her sacrifice and that they will both soon return to ask her forgiveness. Too late, she cries, and in a magnificent aria, she realizes her life will soon be over. Alfredo arrives and for a moment, he convinces her she will recover and again be happy. It is too late for her, and she gives Alfredo a locket that she tells him to give to the woman he will someday meet and marry. She asks him to be happy, and remember her. Reconciled to both father and son, and no longer bound by social convention, Violetta's sacrifice is complete as the curtain falls.