The opening action in the film takes place on the planet Krypton, where, using testimony from the eminent scientist Jor-El, the Ruling Council sentences three insurrectionists, General Zod, Ursa and Non, to "eternal living death" in the Phantom Zone for attempting to install a dictatorship. Following this success, Jor-El attempts to convince the Council of his belief that the Kryptonian sun will shortly explode and destroy their planet, but they dismiss his theory as "outlandish". Threatened with his own imprisonment in the Phantom Zone if he makes his theory public or attempts to flee, Jor-El instead launches a spacecraft containing his infant son, Kal-El, towards Earth, a distant planet with a suitable atmosphere, ensuring he will survive. Minutes after the ship launches, the sun explodes and Krypton is destroyed.

Three years later, the ship reaches Earth, crashing near an American farming town, Smallville, where little Kal-El is found by Jonathan Kent and wife Martha Kent and raised as their own son, Clark. Fifteen years later, after Jonathan Kent suddenly dies, Clark hears a psychic 'call', and discovers it is coming from a glowing green crystal in the remains of his ship. Compelled to travel north, he leaves the homestead and heads to a specific point in the Arctic, where the crystal somehow builds a "Fortress of Solitude", resembling the architecture of Krypton. Activating a control panel inside the fortress, a vision of Jor-El appears before Clark and takes him on a journey through time and space, explaining his origins and educating him in his powers and responsibilities. After twelve years, with his powers fully developed, he leaves the fortress and, as Clark Kent, finds a job at The Daily Planet in Metropolis. He meets and develops a crush upon fellow reporter Lois Lane; his feelings are not returned, but Lois comes to regard Clark as a friend. Shortly afterwards, she is involved in a helicopter accident where conventional means of rescue are impossible, requiring him to use his powers in public for the first time in order to save her. Afterward, Superman has a busy night on his first patrol, stopping crimes and performing more rescues with spectacular effectiveness.

Later, Clark visits Lois at home, takes her for a flight over the city and allows her to interview him for a newspaper article in which she dubs him "Superman." Meanwhile, criminal genius Lex Luthor has developed a cunning plan to make a fortune in real estate, by buying large amounts of 'worthless' western desert land and then diverting a nuclear rocket from a missile testing site to the San Andreas fault line. This will destroy California along with its major cites (San Francisco, Oakland, Fresno, Sacramento, Los Angeles & San Diego), and leave Luthor's desert as the new West Coast, increasing its value exponentially. After his incompetent henchman Otis accidentally redirects the first rocket to the wrong place, Luthor's girlfriend Eve Teschmacher successfully changes the course of a second missile. Realizing Superman could stop his plan, Luthor lures him to his underground hideaway, where he exposes him to Kryptonite, the only substance known to cause him harm. As Superman weakens, Luthor taunts him by revealing the first missile is headed to Hackensack, New Jersey, knowing Superman could not stop both impacts. Miss Teschmacher is horrified by this, as her mother lives in Hackensack, but Luthor does not care and leaves Superman to a slow death.

Miss Teschmacher, after some hesitation, rescues Superman, on the condition that he deals with the New Jersey missile first. He is consequently too late to stop the second impact; the missile explodes, causing a massive earthquake which Superman battles to correct. However, while he is busy saving others, Lois Lane is killed, when the earthquake causes her car to fall into a crevice, and she suffocates from debris. Distraught at being unable to save Lois, Superman flies rapid orbits from east to west around the world, accelerating to super-light speed, rewinding time (represented by the earth appearing to reverse its rotational direction), and ignoring visions of Jor-El warning him not to interfere with human history. He is then able to get to Lois and save her before she dies. Having finally corrected the disaster, Superman delivers Luthor and Otis to prison, until they can get a "fair trial." The Warden tells Superman that the country is safe again, thanks to him. Superman disagrees, saying, "Don't thank me, Warden. We're all a part of the same team. Good night." Flying away into space above the earth, the Man of Steel makes eye contact with the camera and flashes a smile at the audience (a clip which would become the signature for all four Reeve Superman films).