Industrialist John Hammond has created a theme park of cloned dinosaurs, Jurassic Park, on tropical Isla Nublar. After a dinosaur handler is killed by a Velociraptor, the park's investors, represented by lawyer Donald Gennaro, demand a safety certification. Gennaro invites mathematician Ian Malcolm, while Hammond invites paleontologist Alan Grant and paleobotanist Ellie Sattler. Upon arrival, the group is shocked to see a live Brachiosaurus.

At the park's visitor center, the group learns that the cloning was accomplished by extracting dinosaur DNA from prehistoric mosquitoes preserved in amber. DNA from frogs and other animals was used to fill in gaps in the genome of the dinosaurs, and to prevent breeding, all the dinosaurs were made female by direct chromosome manipulation. The group witnesses the hatching of a baby Velociraptor and visits the raptor enclosure. During lunch, the group debates the ethics of cloning and the creation of the park; Malcolm warns about the implications of genetic engineering and scoffs at the park's conceptualization, saying that it will inevitably break down.

Hammond's grandchildren, Lex and Tim, join for a tour of the park, while Hammond oversees from the control room. The tour does not go as planned, with most of the dinosaurs failing to appear and the group encountering a sick Triceratops; it is cut short as a tropical storm approaches. Most of the park employees leave for the mainland on a boat while the visitors return to their electric tour vehicles, except Sattler, who stays behind with the park's veterinarian to study the Triceratops.

Jurassic Park's disgruntled lead computer programmer, Dennis Nedry, has been bribed by Dodgson, a man working for Hammond's corporate rival, to steal fertilized dinosaur embryos. Nedry deactivates the park's security system to gain access to the embryo storage room and stores the embryos inside a container disguised as a shaving cream can. Nedry's sabotage also cuts power to the tour vehicles, stranding them just as they near the park's Tyrannosaurus rex paddock. Most of the park's electric fences are also deactivated, allowing the Tyrannosaurus to escape and attack the group. After the Tyrannosaurus overturns a tour vehicle, it injures Malcolm and devours Gennaro, while Grant, Lex, and Tim escape. On his way to deliver the embryos to the island's docks, Nedry becomes lost in the rain, crashes his Jeep Wrangler, and is killed by a Dilophosaurus.

Sattler helps the game warden, Robert Muldoon, search for survivors; they only find an injured Malcolm, just before the Tyrannosaurus returns and chases them away. Grant, Tim, and Lex take shelter in a treetop and encounter a Brachiosaurus. They later discover the broken shells of dinosaur eggs, and Grant concludes that the dinosaurs have been breeding, which occurred because of their frog DNA—some West African frogs can change their sex in a single-sex environment, allowing the dinosaurs to do so as well.

Unable to decipher Nedry's code to reactivate the security system, Hammond and chief engineer Ray Arnold reboot the park's system. The group shuts down the park's grid and retreats to an emergency bunker while Arnold heads to a maintenance shed to complete the rebooting process. When Arnold fails to return, Sattler and Muldoon head to the shed. They discover the shutdown has deactivated the remaining fences and released the Velociraptors. Muldoon distracts the raptors while Sattler goes to turn the power back on before being