An insurance salesman, Truman Burbank, leads an idyllic, if unremarkable, suburban life in the picturesque town of Seahaven Island. Unbeknownst to him, however, his entire existence is the focus of a 24-hour-a-day TV show broadcast worldwide. Every moment of his life, from birth, has been televised, and all the people in it are actors following a script. Seahaven itself is a massive, high-tech set enclosed in a dome, with Truman the only person not in on the fabricated reality. Cameras hidden everywhere capture his life for the audience's consumption, and the show's manipulative creator directs events to keep Truman oblivious and the show running smoothly.

Truman begins to notice unusual occurrences that challenge his understanding of his world: a spotlight falls from the sky, a radio broadcaster seems to narrate his movements, and an elevator malfunction reveals a backstage area. A series of flashbacks reveals his longing for Sylvia, an extra who tried to reveal the truth to him before being swiftly removed from the show. His growing suspicions and quest for truth lead to increasingly erratic behavior, causing those around him to scramble to maintain the facade. Truman's sense of reality is further challenged as he uncovers more anomalies and inconsistencies, prompting him to question the nature of his existence and embark on a journey to discover the truth about his life.