It is Christmas Eve in an attic apartment shared by four Bohemians. Rodolfo, a poet, and Marcello, a painter, are at home, burning Rodolfo's manuscript in order to stay warm. Colline, a philosopher, enters with some books he unsuccessfully tried to pawn. Soon Schaunard, a musician, comes in brining food, money, and fuel he earned playing for an eccentric Englishman, who challenged him to play until his pet parrot died. As the friends are celebrating, Benoit, the landlord, comes for the rent. The friends give Benoit wine, and he begins to brag about the women he has been with other than his wife. Feigning outrage at his infidelity, they throw Benoit out of the attic without giving him any money for rent. Everyone but Rodolfo, who must write an article, leaves for Cafe Momus. As soon as he is alone, Mimi knocks on the door asking for help because her candle has gone out. Collapsing from a fit of coughing, Mimi, after recovering, realizes she has dropped her key. Then after Rodolfo lights Mimi's candle a breeze extinguishes both candles. Mimi and Rodolfo both search for the key in the dark. Rodolfo finds the key, but he puts it in his pocket so he can spend more time with Mimi. Rodolfo's friends call him from the street, and the first act ends with Mimi and Rodolfo standing in the moonlight of the window singing a love duet.

That same evening, Mimi and Rodolfo walk through a joyous Christmas Eve crowd to the Cafe Momus where they join Rodolfo's friends. Musetta, who used to be Marcello's lover, enters with a wealthy old man, Alcindoro de Mittoneaux. Musetta sings a waltz in order to attract Marcello's attention and make him jealous. Musetta then pretends that her shoe is hurting her and insists that Alcindoro go to the cobbler to get her a new one. Once Alcindoro is gone, Musetta rejoins Marcello and tells the waiter that Alcindoro will pay the bill. Before Alcindoro returns, the friends hurriedly leave the cafe.

At dawn later that winter, Mimi, who is now very frail, makes her way to a toll gate near the edge of the city. She sends a note inside the tavern and Marcello comes out. Marcello asks Mimi to join him, Musetta, and Rodolfo inside the tavern. Mimi explains that she is afraid she can no longer be Rodolfo's lover because he is so jealous. Rodolfo comes out to talk to Marcello, and Mimi hides. Rodolfo confides to Marcello that he doesn't like the frequent arguments he has with Mimi. Rodolfo reveals that he cannot bear to watch her illness slowly claim her life. Mimi coughs and Rodolfo discovers her. They agree, regretfully, to stop their affair. In the meantime, Marcello catches Musetta flirting with another man. The sad farewell duet of Mimi and Rodolfo becomes a quartet as Musetta and Marcello scream insults at each other.

That autumn, back in the Bohemians' apartment, Rodolfo and Marcello sing about how they miss Mimi and Musetta. Shaunard tries to cheer everyone up by pretending to have champagne. Musetta comes in and tells them that Mimi is dying. Mimi is brought to the attic because she wishes to die near Rodolfo. Rodolfo helps Mimi to a cot and tries to warm her hands. Musetta sends Marcello to sell her earrings for medicine. Colline leaves to sell his coat for food, mourning its loss. Musetta leaves to get a muff for Mimi, so that Rodolfo and Mimi are left alone. They sing about how much they loved each other. Their friends return. Mimi falls asleep and then quietly passes away.