In the first scene, set in an unspecified year in the 1820s, Hugh Glass speaks to his son Hawk in an Indian language, telling him that even if he is scared and wants his troubles to end, he must battle for as long as he can catch his breath. As we hear Glass' voice, we see scenes of him with his wife, Pawnee, and son, his home being set on fire, and him holding his wife close.
Glass and Hawk are stalking elk by walking through a river with other hunting team members. They are camped along a river in rural Missouri with other fur trappers. They are led by Captain Andrew Henry. A nude missing man from their party enters the settlement and collapses forward, an arrow in his back. Another man is struck in the neck with an arrow and falls into the campfire. The hunting group is assaulted by the Arikara Indians, also known as 'Ree'. The men shoot back with their weapons. Glass is ambushed and almost strangled to death, but one of his men saves him. A few men pack their furs and tools and head for a boat to make their escape. The Arikaras are searching for the chief's daughter, Powaqa, whom unknown white men kidnaped. The men ditch their boat and begin hiking overland to Fort Kiowa. Hawk gets antagonized by John Fitzgerald because of his race (Hawk is half-Indian on his mother's side), but Glass swiftly defends his son and warns him not to retaliate against Fitzgerald.
While hunting in the woods, Glass encounters a grizzly bear and her cubs and is swiftly mauled by the larger bear. The bear claws and bites Glass, flinging him around as he attempts to defend himself. He successfully shoots the bear, but it does not kill her. She attacks again, and Glass grabs his knife, stabbing it numerous times as they tumble down a hill. Glass lands in a gully, and the dead bear falls on top of him. The men subsequently discover Glass and attempt to treat his terrible wounds.
Meanwhile, the Arikara warriors continue to search for Powaqa. They meet French fur traders and exchange the riverbank furs for five horses.
The men in the hunting group transport Glass on a homemade stretcher, but he delays their progress. They try to carry him up a slope, but he slides and brings the other men down. Fitzgerald recommends they kill Glass and put him out of his misery. Henry covers Glass's eyes and nearly shoots him in the head, but he can't bring himself to do it. Henry gives $75 to anyone who stays behind with Glass. Hawk and Jim Bridger volunteer, but Fitzgerald warns that they and Glass are sure to die. Henry raises the price offer to $100, and Fitzgerald agrees to continue with them until Glass expires.
Glass is still in a lot of sorrow and has vivid memories of his wife and the day his house burned down.
Fitzgerald has a moment alone with Glass and attempts to persuade him to let him put him out of his suffering so that no one else, including Hawk, is slowed or left waiting to die. As Glass is unable to speak, Fitzgerald suggests that Glass blink if he agrees, knowing that Glass would eventually have to blink, with or without intent to agree to Fitzgerald's offer. Instead of blinking, he keeps his eyes wide for an extended period before closing them. Fitzgerald purposefully sees this as blinking and begins to smother Glass. Hawk arrives, discovering Fitzgerald choking his father. Hawk begins to call Bridger for assistance, resulting in a struggle with Fitzgerald in which the man stabs Hawk in the abdomen and then lets him bleed out while Glass watches helplessly. Fitzgerald disposes of Hawk's body and tells Bridger that he has no idea where he went.
Later that night, Fitzgerald begs Bridger to accompany him, claiming to have seen Ree Indians near the creek. Fitzgerald has already dug a grave for Glass and roughly takes him into it, partially burying him alive under a pile of earth, which Bridger unwillingly allows.
Meanwhile, Henry and the rest of the hunting party face an arduous march to Fort Kiowa. Glass awakens, struggling to emerge from the mud. He starts creeping through the woods, looking for food and warmth. He discovers Hawk's body thawing from the cold. Glass promises to stay by his son's side. As Fitzgerald and Bridger approach them, Bridger realizes Fitzgerald has lied about seeing the Ree at the creek. He directs his rifle towards Fitzgerald, who takes it from Bridger and turns it on him. He pulls the trigger, but the unloaded weapon registers an empty chamber. They continue to move.
Glass chooses to move from there. He takes the bear claw pendant from his son. He takes a thick bear pelt with him to keep warm. As he crawls through the woods, he eats roots and old bone marrow. The Indians are getting closer, following the traces. He tries to start a fire for warmth and uses some of his remaining gunpowder to seal the wound in his throat. Indians attack Glass when they trace him; Glass escapes and rides down the rapids to escape.
Fitzgerald and Bridger are continuing to walk. They come to discover a burned-out village with bodies scattered across the ground. One woman emerges from her burning hut and notices the men. Bridger quietly leaves food for her.
Glass is becoming colder and hungrier. He wades into the river and eats a live fish. He travels up a hill and sees a Pawnee Indian eating a bison carcass. Glass approaches him warily and motions for food. The Indian throws him an organ, which Glass devours. In the morning, the Indian notices the bear wounds on Glass' body, which are beginning to decay. Glass claims his men abandoned him for dead and murdered his son. The Indian claims that his own family was murdered by a rival Sioux tribe. He says he is looking for more Pawnee. Glass and the Indian move on.
Fitzgerald and Bridger reach the station and rejoin their companions. Fitzgerald tells Henry that they were unable to save Glass or Hawk, and he receives his reward. Bridger remains silent, but he is unhappy and declines a bonus payment.
Glass and the Indian spend the evening reclining and gathering snow in their jaws; it's the first time Glass has appeared serene in a while. The Indian arranges supplies for a quick sweat lodge and inserts a feverish Glass inside. The Pawnee conducts a healing rite for Glass' wounds. Glass begins to hear his wife's voice and then sees himself approaching Hawk before they hug in an old church.
When Glass awakens, the Pawnee is gone. A short while later, he discovers that the Indian has been hanged by French fur trappers. He infiltrates their tent and sees one of the men rape a woman. And that woman is Powaqa. Glass holds the rapist at gunpoint before freeing Powaqa. Glass then takes a horse and sets the other horses free. He rides to a location in the woods and sets himself on fire.
In the morning, the tribe seeking Powaqa begins to attack. Glass holds them off with his rifle before mounting his horse and riding away. The tribe rides their horses up to a point where Glass and his horse go over the edge. The horse dies, and Glass is injured again. As the night falls and the cold worsens, he cuts the horse open, extracts its organs, and sleeps inside its carcass for warmth. When he wakes up, he exits the carcass and goes to a snow cave. In there, he writes, "Fitzgerald killed my son."
Later, at the outpost, one of the French hunters arrives with Glass' can, which Bridger had left on the dirt pile when Fitzgerald buried him. Henry leads a search party across the woods, convinced he got it from Hawk. They discover Glass limping towards them. They rescue him and return him to the outpost. Henry discovers that Fitzgerald has left. The French hunter informs him that Fitzgerald is heading to Texas. Fitzgerald also cleaned out the party's payroll safe. Henry then attacks Bridger with his rifle, beating him to the ground before putting him in the stockade.
Glass defends Bridger's innocence to Henry, claiming that he was simply following orders. He also tells Henry how he witnessed Fitzgerald murder his kid. When Glass learns that Fitzgerald is on his way to Texas, he suggests he go find him. Henry grudgingly agrees to have Glass accompany him on the hunt.
To meet Fitzgerald, the two men split off to pursue him from opposing sides. Henry discovers Fitzgerald first and intends to bring him back to stand a murder trial. Fitzgerald draws his revolver and kills Henry. Glass discovers Henry's body and places him back on top of his horse, using a branch as a prop. They continue riding in front of Fitzgerald, who fires his gun from afar. He thinks he murdered Glass, but he shoots Henry's body. Glass fires a shot and wounds Fitzgerald, who flees as Glass pursues. Fitzgerald shoots Glass when they are cornered in the woods.
Fitzgerald flees down by the creek, where Glass confronts him, and they begin to fight. Fitzgerald almost stabs Glass, but he turns the knife on him. Fitzgerald impales Glass' hand, but Glass overcomes him and nearly kills him before Fitzgerald admits that murdering him will not bring his son back. On the other side of the creek, Glass notices the Indians pursuing him, along with Powaqa. He determines that revenge is in God's hands, so he puts Fitzgerald into the river and allows him to float across to the Indians. The chief seizes Fitzgerald and kills him with his knife. They spare Glass because Powaqa informs them that Glass has freed her.
Despite having earned his retribution, Glass is now again alone, wandering through the chilly land. He falls to his knees and sees his wife walking into the light again. The final shot shows Glass' eyes brimming with tears.
