Ex-soldier Jeremiah Johnson (Robert Redford) decides that he would rather live alone as a mountain man in Colorado than deal with civilization's restrictions. After many setbacks, he meets grizzled mountain man Bear Claws (Will Geer), who teaches him how to survive.
Jeremiah strives to live as peaceably as possible in the rough environment, trading with the native Crow tribe, adopting a boy he names Caleb (Josh Albee), who is rendered mute after seeing his family murdered, and even marrying the daughter (Delle Bolton) of a Flathead Chief to avoid a battle. Together, they build a mountain home and become a happy family.
The U.S. cavalry, complete with a callous Reverend, interrupts the happiness to force Jeremiah to lead them over the mountains and through a Crow burial ground to rescue a wagon train of white settlers.
After the Crow kills his family in revenge, Jeremiah's moment of payback starts a long-running battle, turning him into a renowned Indian killer at the expense of his original morals.
Johnson drifts on, and finally, at a distance, faces a Crow brave he’d met when he was still a struggling, half-frozen mountain greenhorn — Paints His Shirt Red (Joaquin Martinez). Johnson begins to reach for his rifle but holds as Paints His Shirt Red raises his hand in peace. Johnson reaches his own hand out as if to touch the brave. It seems the war is finally over.
Shot on location in Utah, the film captures both the appeal and the challenge of the land that Jeremiah chooses over civilization.