On the planet Krypton, Jor-El of the Kryptonian high council believes that their planet will soon be destroyed when its red supergiant sun goes supernova. Despite his eminence, he fails to convince the other council members. To save his infant son, Kal-El, Jor-El launches him in a spaceship to Earth, a planet with a suitable atmosphere where his dense molecular structure will give him superhuman powers. Shortly after the launch, Krypton's sun explodes, destroying the planet.
The ship crash lands on Earth near Smallville, Kansas. Kal-El, who is now three years old, is found by Jonathan and Martha Kent, who are astonished when he lifts their truck. They take him to their farm and raise him as their own, naming him Clark after Martha's maiden name.
At 18, soon after Jonathan's death from a heart attack, Clark hears a psychic "call" and discovers a glowing crystal in the remains of his spacecraft. It compels him to travel to the Arctic, where it builds the Fortress of Solitude. Inside, a hologram of Jor-El explains Clark's true origins, and after 12 further years of educating him on his powers and his reason for being sent to Earth, he leaves the Fortress wearing a blue and red suit with the House of El family crest on his chest and becomes a reporter at the Daily Planet in Metropolis. He meets and develops an unrequited romantic attraction to coworker Lois Lane.
Lois becomes involved in a helicopter accident where conventional means of rescue are impossible, requiring Clark to use his powers in public for the first time to save her to the astonishment of the crowd gathered below. He then goes on to thwart a jewel thief attempting to scale the Solow Building, captures robbers fleeing police through the Fulton Market by depositing their cabin cruiser on Wall Street, and rescuing a girl's cat from a tree in Brooklyn Heights. He even saves Air Force One after a lightning strike destroys the port outboard engine, making the "caped wonder" an instant celebrity. Clark later visits Lois at her house the next night and takes her for a flight over the city, allowing her to interview him for an article in which she names him "Superman".
Meanwhile, criminal genius Lex Luthor learns of a joint U.S. Army and U.S. Navy missile test. He then buys hundreds of acres of worthless desert land and reprograms one of the warheads to detonate in the San Andreas Fault, sinking California and leaving Lex's desert as the new West Coast.
Knowing Superman could stop his plan, Lex deduces that a meteorite found in Addis Ababa is actually part of Krypton, and after he and his accomplices Otis and Eve Teschmacher retrieve a piece of it, Lex lures Superman to his underground lair, reveals his plan and exposes him to a mineral from the meteor, Kryptonite, which weakens Superman greatly. Lex further taunts him by revealing that the other warhead is headed in the eastbound direction toward Hackensack, New Jersey. Teschmacher is horrified because her mother lives in Hackensack, but Lex does not care and leaves Superman to a slow death. Knowing his reputation for keeping his word, Teschmacher rescues Superman on the condition he will deal with the New Jersey missile first. Superman diverts the eastbound warhead into outer space, but can't reach the other missile in time, and it explodes in the San Andreas Fault. Superman mitigates the effects of the explosion, getting rid of the fallout and shoring up the crumbling Earth, but the aftershocks damage the Golden Gate Bridge and cause the Hollywood Sign and the Hoover Dam to collapse, endangering lives.
While Superman is busy saving others, Lois's car ends up falling into a crevice from one of the aftershocks. It fills with dirt and debris and she suffocates. Angered at being unable to save her, Superman defies Jor-El's earlier warning not to manipulate human history, preferring to heed Jonathan's advice that he must be here for "a reason". He accelerates around Earth, rewinding time, to save Lois. After bringing Lex and Otis to prison, he flies into the sunrise for further adventures.