On the planet Krypton, Jor-El, a member of the Kryptonian high council, sentences criminals General Zod, Non, and Ursa to the Phantom Zone. He warns the council that Krypton will be destroyed by its exploding red supergiant sun, but they dismiss his concerns. Before the planet's destruction, Jor-El and his wife Lara send their baby son Kal-El to Earth, where his unique physiology grants him evolving superhuman abilities. Kal-El's spaceship touches down near Smallville, Kansas. Found by Jonathan and Martha Kent, who are astonished when the infant lifts their truck, they adopt him, naming him Clark. As he grows, hiding his powers, Jonathan believes Clark was sent to Earth for a special purpose.

Soon after Jonathan's fatal heart attack, a glowing green crystal from his spaceship that is hidden in the barn calls to Clark. This leads him to the Arctic, where a Fortress of Solitude, echoing Krypton's architecture, ascends from the ice. Inside, Jor-El's hologram reveals Clark's heritage and trains him for twelve years. Emerging in a blue-and-red suit bearing the House of El crest, he is cautioned against changing human history. Clark is hired as a reporter for the Daily Planet in Metropolis. He is drawn to Lois Lane. After saving her from a helicopter accident, Clark secretly uses his powers in public acts of heroism, gaining immediate fame as the "caped wonder". Perry White, the Daily Planet's chief, seeks more information on this new hero. Clark later visits Lois, taking her on a flight, leading her to coin his name, "Superman". Criminal mastermind Lex Luthor discovers a joint U.S. Army/U.S. Navy missile test and plots to target the San Andreas Fault with reprogrammed missiles, though one is misdirected by his bumbling assistant, Otis. Suspecting Superman's interference, Lex identifies a Kryptonian meteorite, lethal to Superman. With Otis and his girlfriend Eve Teschmacher, Lex retrieves it and traps Superman in his lair, revealing his plan to sink the western U.S., making his desert land prime coastline. He weakens Superman using the meteor, now known as Kryptonite, and informs him of the misdirected missile set for Hackensack, New Jersey.

Concerned for her mother in Hackensack, Teschmacher frees Superman, urging him to first stop the eastbound missile. He sends it to space but misses the westbound missile, which triggers severe earthquakes in California, endangering landmarks like the Golden Gate Bridge and Hoover Dam. Superman counteracts the devastation by mending the fault line. As Superman rescues others, Lois is trapped in her car by an aftershock, suffocating before he can save her. Distraught and enraged over his failure to save Lois, Superman disregards Jor-El's warning against altering history. Heeding Jonathan's belief in his purpose, he flies around Earth, reversing time to prevent Lois's death and the missile's destruction. After saving the West Coast, he imprisons Luthor and Otis, then soars into the sunrise.