In 1845 in North-Western Territory, British North America, young James Howlett (Troye Sivan) sees his father John Howlett (Peter O'Brien) killed by his friend Victor Creed's father, Thomas Logan (Aaron Jeffery). In an act of vengeance, James kills the elder Logan using bone claws which have grown out of his hands. With his dying breath, Logan tells James that he is also his son. James and Victor (Michael-James Olsen) run away, pursued by a torch-wielding mob. They promise to look out for each other.

In the years that follow, adult brothers James (Hugh Jackman) and Victor (Liev Schreiber) are seen fighting together in the American Civil War, World War I, World War II, and eventually the Vietnam War. Their regenerative powers keep them from being killed in the battlefield. James is forced to act as a check on Victor's increasing rage and ferocity. In Vietnam, Victor kills a superior officer after being stopped from raping a girl, and James and Victor are sentenced to death by firing squad, though their unique regenerative abilities keep them alive.