Christof, the creator of a television show called "The Truman Show," informs a documentary-style camera that even though everything around Truman is fake, his life and emotions are genuine. Actors Hannah Gill and Louis Coltrane, who play Truman's wife and best friend, respectively, support Christof's statement. Meanwhile, Truman Burbank (Jim Carrey) has no idea that 5,000 hidden cameras document his entire life, making him one of the biggest TV stars in the world. He also does not realize that Seahaven Island, where he lives, is a giant television studio under a dome, controlled entirely by Christof and his production team.
Truman is a cheerful insurance adjustor with a pretty, perky wife, Meryl. One morning, a cinema light falls in front of his house but a subsequent radio broadcast explains it away by claiming that a plane flying overhead had been shedding parts. At work, Truman tries to make a secret phone call to Fiji looking for someone named Lauren or Sylvia Garland. He can't find her. Later, his boss instructs Truman to go to Wells Island to meet a client. This will require Truman to take a ferry, but he's desperately afraid of the water, so he turns back.
Truman tells his friend Marlon about his dream to go to Fiji, but Marlon convinces Truman that his life on Seahaven Island is enviable, trying to dissuade him from leaving. Later, Truman sits at home on the beach and "The Truman Show" cuts to a flashback of Truman's father drowning at sea. Back in the present, the rain starts to fall - just on Truman. As soon as he realizes this, the whole sky opens up. Back at home, a soaking wet Truman tries to convince Meryl to leave everything behind and roam around the world, but she dismisses the idea as absurd and seduces him into bed instead.
The next day, on his way to work, Truman sees a hobo who looks exactly like his father. Before he can speak to the man, some other pedestrians take the man away and bundle him onto a bus. Later, Truman goes to visit his mother, Angela, who dismisses the encounter as a vision stemming from the loss of his father.
In his basement, Truman goes through a box of keepsakes, including a red sweater. It belonged to a woman named Lauren (or Sylvia) that Truman fell for in high school. She was supposed to be an extra but she caught Truman's eye. However, Meryl was his intended mate, so "The Truman Show" producers did everything in their power to keep Lauren and Truman apart. One night, Truman and Lauren are able to steal a kiss on the beach, and Lauren tells Truman that her real name is Sylvia and tries to reveal the truth. Before Truman can digest what's happening, though, Lauren's "father" barrels onto the beach and takes her away, saying she's insane and they're moving to Fiji. Truman's viewers at "The Truman Bar" are still invested in this romantic storyline (just like Truman himself).
The next day, Truman overhears the production walkie-talkies on his radio, describing his exact location. He is paranoid now, despite the "radio announcer's" explanation that there was an interference with a police scanner. Truman does not go into the office, and wanders around Seahaven instead, finally noticing all the strange things happening around him that he never saw before. Extras are lunching in an elevator shaft, and buses and cars stop for him as he crosses the street. He tries to talk to Marlon, who treats Truman like he is unraveling. Truman, however, insists that he's going away for a while. The next morning, he follows Meryl to work, forcing her and the actors playing doctors to bungle their way through a fake "surgery." Truman leaves a message for Meryl to say that he's going to Fiji.
Truman tries many different methods to get out of Seahaven, but Christof is able to stop him at every turn. Finally, he forces Meryl to come with him and points out all the strange inconsistencies in his life. He eventually runs out of the car at a roadblock, but a group of extras wrestle him to the ground and return him to his home. When Meryl tries to act out her scripted product placement for "Mococoa," Truman insists on knowing who she is talking to. His paranoia gets the better of him and he threatens her by holding a sharp utensil to her throat. Finally Marlon comes over with a six-pack and saves Meryl, who bawls that the situation has become "unprofessional."
That night, Marlon makes a heartfelt speech to Truman, trying to convince him that his paranoia is unfounded. However, Christof is telling Marlon exactly what to say through an earpiece, including, "I would never lie to you, Truman." Marlon reveals that Truman was, indeed, right about his father. Kirk comes out of the fog to hug his son - they are going with the story that he has had amnesia for the past 22 years but has come back. On a televised interview with Christof, the creator describes the mechanisms that have kept "The Truman Show" running for the past 29 years without Truman's knowledge. Everything on the show is for sale, and actors integrate product placement regularly (as we have seen before). Lauren/Sylvia calls into the show to tell Christof he is manipulative and evil, but Christof assures her that Truman "prefers his cell" to the sick world outside of it.
Late one night, Truman is asleep in the basement, where he has moved after Meryl left. Suddenly, the "The Truman Show" control team realizes that Truman is not actually there - he has escaped their cameras. Christof cuts transmission for the first time. They mount an Island-wide search, and Christof even turns on the "sun" to make it easier. However, by this time, Truman is actually on a boat in the middle of the ocean, having overcome his fear in order to achieve his dreams. Christof creates a massive storm and seems to be ready to kill Truman to keep him from figuring out the truth. Eventually, Christof is forced to introduce himself to Truman - only as a voice from the sky, though. He tries to prevent Truman from leaving the safety of Seahaven, saying that what lies outside is sick and dangerous. Truman, however, tells Christof that he never had cameras in his head and doesn't know Truman as well as he thinks he does.
Truman then steps off the set for the first and last time. His loyal viewership applauds, celebrates and... changes the channel, looking for something else to watch.