In the courtyard of a German inn, the townspeople have gathered. Lothario, a wandering minstrel, sings. Philine and Laertes, on their way to give a theatrical performance, appear on a balcony. Mignon is sleeping in the back of a gypsy cart. Jarno, chief of the gypsy band, rouses her. She refuses to dance. He threatens her with a stick. Lothario and Wilhelm protect her and she divides a bouquet of wild flowers between the two. Wilhelm, greatly impressed with Mignon’s beauty, does not mind when Laertes takes the flowers from him and hands them to Philine.

Mignon tells Wilhelm of her childhood and the land from which she was abducted. Wilhelm decides to purchase her freedom and enters the inn with Jarno to conclude the negotiations. Mignon, overjoyed at the prospect of liberty, shares her delight with Lothario. Mignon wishes to remain in the service of Wilhelm but Lothario wants to take her with him. Wilhelm does consent to care for her as long as she disguises herself as a page. The act ends as the actors depart for Rosenberg’s castle and their evening performance.

Philine is seated at a mirror in her dressing room. Wilhelm enters followed by Mignon, now dressed as a page. Mignon feigns sleep until Wilhelm and Philine leave, then, in an effort to make herself more attractive to Wilhelm, she toys with Philine’s makeup and enters the actress’s wardrobe to try on one of her gowns. Frederic enters in search of Philine, and Wilhelm enters to find Mignon. The two men meet and are about to fight, when Mignon rushes between them. Wilhelm, realizing the awkward situation, tells her they must part. Philine re-enters and makes sarcastic remarks to Mignon about her appearance. Mignon tears the gown from herself, and as Wilhelm and Philine are leaving she declares her hatred for Philine.

The scene changes to Baron von Rosenberg’s park. Mignon is about to throw herself into the lake when she hears Lothario’s harp. Upon recognizing Mignon, he commiserates with her. Applause rings out from the conservatory for Philine’s acting. Mignon, dashing off, calls upon divine thunderbolts to bring the castle down upon the actress’s head. Lothario insanely takes this as an order, and wanders off babbling about “the fire.”

They have been playing A Midsummer Night’s Dream and Philine is flushed with success. She looks for Wilhelm, who in turn looks for Mignon. Lothario finds Mignon and whispers that her command has been obeyed. When Philine, unaware of the arson, asks for the bouquet she left in the conservatory, Mignon goes in to get it. The conservatory is seen to be in flames. In the ensuing panic, Wilhelm charges into the flames to rescue Mignon, and appears soon after with the stricken girl in his arms. Her hand still holds a bunch of withered flowers.

Wilhelm has brought Lothario and the dangerously ill Mignon to an Italian castle. As a boating chorus is heard from the lake below, Wilhelm tells Lothario that they are in the Cipriani castle, which he intends to buy for Mignon. At the name of the castle Lothario is strangely agitated. Mignon is ecstatic.

In the scenes that follow, Lothario, his reason restored by being again in familiar surroundings, recognizes in the place his own castle and in Mignon his daughter, whose loss had unsettled his mind. The opera closes with a joyful trio for Mignon, Wilhelm, and Lothario.