Harold Crick (Will Farrell) is an IRS auditor who almost compulsively measures, quantifies and rationalizes his life. Suddenly, he becomes aware of a voice narrating his life, "accurately and with a better vocabulary." The voice is that of a writer we learn is struggling with writer's block (Emma Thompson), mostly about the best way to make Harold die. When Harold overhears his impending doom, he takes action, and eventually makes his way to a professor of literary theory (Dustin Hoffman), who helps him understand the implications of the narrative life he is leading. The main story line seems to be around a woman he is auditing, played by Maggie Gyllenhaal. Realizing he could die at any moment, Harold begins to break free of his limited, orderly life, and joins Gyllenhaal in a romantic relationship. He tracks down Thompson and confronts her with the truth: if she writes about his death, then he will die. But Hoffman is convinced the novel must be written as intended, and Thompson herself is ambivalent. Crick himself reads the novel and encourages her to keep the original ending, which would kill him.
Eventually, Thompson writes of the fatal accident, but makes the accident only near-fatal. "If you have someone who willingly, knowingly, goes to his death, well...isn't that the kind of person you want to keep alive?" In the end, there is an ode to Harold, Maggie, Dustin, and most of all, Harold's wristwatch.