Two men arrive separately in 1984 Los Angeles, having time traveled from 2029. One is a cybernetic assassin known as a Terminator, programmed to hunt and kill a woman named Sarah Connor. The other is a human soldier named Kyle Reese, intent on stopping it. They both steal guns and clothing.
The Terminator systematically kills women bearing its target's name, having found their addresses in a telephone directory. It tracks the last Sarah Connor, its actual target, to a nightclub, but Reese rescues her. The pair steal a car and escape, with the Terminator pursuing them in a stolen police car.
As they hide in a parking lot, Reese explains to Sarah that an artificially intelligent defense network known as Skynet, created by Cyberdyne Systems, will become self-aware in the near future and trigger a global nuclear war to exterminate the human species. Sarah's future son (John Connor) will rally the survivors and lead a successful resistance movement against Skynet and its army of machines. On the verge of the resistance's victory, Skynet sent the Terminator back in time to kill Sarah and prevent John from being born. The Terminator is an efficient and relentless killing machine with a perfect voice-mimicking ability and a durable metal endoskeleton covered by living tissue that disguises it as a human.
Police apprehend Reese and Sarah after another encounter with the Terminator. It attacks the police station, killing police officers while hunting for Sarah. Reese and Sarah escape, steal another car, and take refuge in a motel, where they assemble several pipe bombs and plan their next move. Reese admits that he has adored Sarah since he saw her in a photograph John gave him and that he traveled through time out of love for her. Reciprocating his feelings, Sarah kisses him and they have sex, conceiving John.
The Terminator locates Sarah by intercepting a call intended for her mother. She and Reese escape the motel in a pickup while it pursues them on a motorcycle. In the ensuing chase, Reese is badly wounded by gunfire while throwing pipe bombs at the Terminator. Sarah knocks the Terminator off its motorcycle but loses control of the truck, which flips over.
The Terminator, now bloodied and badly damaged, hijacks a tank truck and attempts to run down Sarah, but Reese slides a pipe bomb into the tanker's hose tube, causing a giant explosion that burns all the flesh from the Terminator's endoskeleton. It pursues them into a factory, where Reese activates the machinery to confuse it. He jams his final pipe bomb into its midsection, blowing it apart at the cost of his life. Its still-functional torso grabs Sarah, but she breaks free and lures it into a hydraulic press, crushing and finally destroying it.
Months later, Sarah, pregnant with John, travels through Mexico, recording audio tapes to pass on to him. At a gas station, a boy takes a polaroid picture of her, and she buys it. It is the exact photograph that John will one day give to Reese.