Riggan Thomson is a faded actor famous for playing a superhero named Birdman in a film trilogy in the 1990s. He is tormented by the mocking and critical internal voice of Birdman and frequently visualizes himself performing feats of levitation and telekinesis. Riggan is trying to regain recognition by writing, directing, and starring in a Broadway adaptation of Raymond Carver’s short story, “What We Talk About When We Talk About Love.” However, the Birdman voice wants Riggan to return to blockbuster cinema and insists that he is an essential part of Riggan’s identity.

Jake, Riggan’s best friend and lawyer, is producing the play, which co-stars Riggan’s girlfriend, Laura, and Broadway débutante Lesley. Riggan’s daughter Sam, a recovering drug addict with whom he is trying to reconnect, is working as his assistant. The day before the first preview, a light fixture falls onto Riggan’s hapless co-star, Ralph. At Lesley’s suggestion, Riggan replaces Ralph with her boyfriend, the brilliant but volatile and self-absorbed method actor Mike Shiner. The first previews are disastrous: Mike breaks character over the replacement of his gin with water, attempts to rape Lesley during a sex scene, and claims that the prop gun does not look real. Riggan clashes continually with Mike, culminating in a brawl after Riggan reads a New York Times interview with Mike in which he steals Riggan’s personal reason for doing a Raymond Carver play. Jake persuades Riggan to continue with the play. When Riggan berates Sam after finding her using marijuana, she insultingly rebukes and chastises him, telling him he is irrelevant and the play is for his own vanity.

During the final preview, Riggan accidentally locks himself outside with his robe stuck in the fire escape door. He is forced to walk through Times Square in his white briefs and enter through the audience to do the final scene. A concerned Sam is waiting in his dressing room after the show. She thinks the performance was very unusual but interesting. She shows him that the Times Square footage is going viral and explains how this actually helps him.

Riggan goes to a bar for a drink and approaches Tabitha Dickinson, a cynical and highly influential theater critic. She promises to “kill” his play with a deprecating review without even having seen it. On the way back, Riggan buys a pint of whiskey, drinks it, and passes out on a stoop. The next day, walking to the theater with a severe hangover, he visualizes Birdman trying to convince him to abandon the play and make a fourth Birdman film. Riggan then imagines himself flying through the streets of Manhattan before arriving at the theater.

On opening night, the play is going very well. In his dressing room, a strangely calm Riggan confesses to his ex-wife, Sylvia, that several years ago he attempted to drown himself in the ocean after she caught him having an affair. He also tells her about the Birdman voice, which she ignores. After Sylvia leaves, Riggan picks up a real gun for the final scene in which his character commits suicide. At the climax, Riggan shoots himself in the head on stage. The play receives a standing ovation.

Riggan wakes up in a hospital — the suicide attempt merely blew off his nose, which has been surgically reconstructed. Tabitha has published a glowing review of the play, calling the suicide attempt just what American theater needed. Sam visits with flowers and takes a picture of him to share with the skyrocketing number of followers on the Twitter account she has created for him. While she steps outside to find a vase, Riggan goes into the bathroom, removes the bandages revealing his swollen new nose, and says goodbye to Birdman, seen seated on the toilet. Fascinated by the birds flying outside his room, he opens the window, peers up at them, and then climbs out onto the ledge. Sam returns to an empty room and frantically runs to the open window, scanning the ground before slowly looking up into the sky and smiling.