In 1823, a crew of trappers under the command of Captain Andrew Henry hunt for pelts in the wilderness of the Northern Plains, inunorganized U.S. territory (later the Dakotas). When Arikara Native Americans launch a surprise attack on the party’s camp, many of the trappers are slaughtered and the survivors flee on a boat. At the recommendation of the party’s experienced guide Hugh Glass, they abandon the boat and begin the journey back to their outpost, Fort Kiowa, on foot. The decision bothers some, particularly John Fitzgerald, who is hostile towards Glass and Glass’s half-native son Hawk, since he was partially scalped by natives years earlier.
While scouting ahead alone, Glass disturbs a grizzly bear and, though he manages to kill the bear, is badly mauled. The party discovers him close to death and carries him on a makeshift stretcher. Fitzgerald argues that Glass will not survive his injuries and that they should kill him to speed their journey. Unwilling to kill Glass, Henry offers payment to those who will stay behind with him instead. Fitzgerald, Hawk, and the young Jim Bridger volunteer. Henry makes Fitzgerald promise to stay with Glass until he dies and give him a proper burial.
Once alone with Glass, Fitzgerald tries to smother him, but Hawk discovers them. A struggle ensues and Fitzgerald kills Hawk while Glass watches helplessly. When Bridger returns, Fitzgerald says Hawk is missing, and Glass is too injured to protest. Fitzgerald lies that the Arikara are nearby and that they must abandon Glass; he drags Glass into a shallow grave. Bridger hesitates, but flees with Fitzgerald, leaving Glass with his canteen. Glass crawls from the grave and walks for days, slowly regaining strength and haunted by visions of his deceased Native wife. He escapes the Arikara, whose chief is searching for his kidnapped daughter Powaqa, by floating down rapids.
On their way to Fort Kiowa, Bridger realizes that Fitzgerald lied but Fitzgerald intimidates him into silence. When they arrive at the fort, Fitzgerald tells Henry that Glass succumbed to his wounds and that Hawk was likely attacked by the Arikara. Henry pays Fitzgerald his reward, but Bridger refuses payment.
Glass encounters Hikuc, a friendly Pawnee who shares bison meat with him. Hikuc has lost his family too, but says that “revenge is in the Creator’s hands”. They travel on horseback. Hikuc treats Glass’s infections with maggot therapy and shelters him in a makeshift tent. Glass wakes the next morning to find Hikuc hanged by a group of French pelt hunters. He infiltrates their camp and sees the leader raping Powaqa. He frees her, kills two hunters, and retakes Hikuc’s horse, leaving behind Bridger’s canteen. He encounters the Arikara again and escapes by galloping off a cliff, killing the horse and injuring himself further. He survives the night by sheltering inside the horse’s carcass.
At Fort Kiowa, a lone French hunter arrives carrying Bridger’s canteen. Believing it was stolen from Hawk, Henry organizes a search party and leaves to find him. Fitzgerald, realizing that Glass is alive, steals the fort’s money and escapes. Henry’s search party discovers Glass and brings him to the fort. Furious, Henry charges Bridger with treason, but Glass assures Henry that Fitzgerald lied to him. Glass insists on joining Henry to find Fitzgerald. After they split up, Fitzgerald ambushes Henry. Glass finds Henry dead and scalped.
By pretending to be dead, Glass ambushes Fitzgerald and shoots him in his shoulder. He chases him into the woods and they engage in a bloody fight beside a river. Glass is about to kill Fitzgerald, but remembers Hikuc’s words and pushes him downstream into the hands of the Arikara. The chief, accompanied by Powaqa, scalps and kills Fitzgerald, but spares Glass. Glass walks away and sees a vision of his deceased wife.