As morning sunlight streams into her boudoir, The Princess von Werdenberg (the Marschallin) is embraced by Octavian, her young lover. The youth hides when a little blackamoor, Mohamed, enters with a tray of breakfast chocolate. At the sound of voices in the antechamber, the Marschallin at first fears that her husband has returned unexpectedly, but it is instead her country cousin, the coarse Baron Ochs auf Lerchenau. Octavian, to amuse himself and avoid discovery, dons the dress of a chambermaid, “Mariandel.” The baron barges in and begins to discuss his pending marriage to Sophie von Faninal, daughter of a wealthy bourgeois; he is looking for a knight to present a silver rose in token of the engagement. During the conversation, Ochs flirts with Mariandel. The Marschallin slyly suggests Octavian as the bearer of the rose and shows his picture to the baron, who is struck by its resemblance to the chambermaid. As the room fills with retainers and petitioners for the Marschallin’s levée, Mariandel escapes. A singer offers a sentimental aria, cut short by the baron’s wrangling with a lawyer over Sophie’s dowry. The baron hires a pair of Italian intriguers, Annina and Valzacchi, to locate Mariandel. When the room is cleared, the Marschallin muses on her waning youth. Octavian returns and is perplexed by her wistful mood. Stunned when she suggests that one day he will tire of her, he leaves without a kiss. The Marschallin tries to call him back, but he is already on the road. Summoning Mohamed, the Marschallin sends Octavian the silver rose.
In the ostentatious reception hall of von Faninal’s town palace, he and Sophie excitedly await the baron’s cavalier while the girl’s duenna, Marianne, stands by a window describing the arrival of the coach. Octavian enters in magnificent attire and presents the silver rose to Sophie, who accepts rapturously. After a few words of polite conversation, chaperoned by Marianne, the two young people feel attracted to each other. Ochs enters, shocking Sophie with his crudity before going off to discuss technicalities with her father. As Octavian embraces her, they are seized by Annina and Valzacchi, who summon Ochs. Octavian, protecting Sophie’s honor, draws his sword and scratches the baron’s arm. Amid the ensuing confusion, von Faninal is enraged to hear Sophie declare she will never wed Ochs. Meanwhile, Octavian enlists the services of Annina and Valzacchi. The baron soothes his wounded vanity with wine. As it begins to take effect, Annina appears with a note from Mariandel asking for a rendezvous. Ochs, intoxicated with his own charm and anticipating an amorous conquest, ignores Annina’s hints for a tip.
At Octavian’s instigation, Annina and Valzacchi help prepare a room in a dingy inn. Before long, Ochs and Mariandel arrive for a private supper. As the counterfeit chambermaid coyly leads her suitor on, grotesque heads pop out of trapdoors and secret panels, unnerving the baron. Annina, disguised as a widow, runs in crying that Ochs is the father of her many children. The police arrive, followed by von Faninal, who summons Sophie to disprove the baron’s claim that Mariandel is his legitimate fiancée. As Octavian whispers his identity to the officer, the Marschallin enters. She forces the baron to renounce Sophie and dismisses him. He leaves, pursued by waiters, clamoring for payment. The Marschallin, lamenting that she must relinquish her lover so soon, gives the bewildered Octavian to Sophie. She slips unnoticed from the room as the young people marvel at their dream come true. With von Faninal, the Marschallin passes by in a last farewell. Octavian and Sophie renew their vows and run from the room. Sent by the Marschallin to retrieve Sophie’s dropped handkerchief, Mohamad finds it and trips out.