"Jack," the film's narrator (EDWARD NORTON), is a disillusioned recall investigator for a major automobile manufacturer. Bored with his Ikea-dominated life and suffering from insomnia, he takes a doctor's advice and begins attending various support group meetings to encounter people who really have problems. At such a group for testicular cancer survivors, he meets Bob Paulsen (MEAT LOAF), a large man with even larger enlarged breasts, and soon finds himself addicted to such meetings for the cathartic release they elicit.
His solution is ruined, however, when he notices that Marla Singer (HELENA BONHAM CARTER), a chain-smoking "tourist," is similarly attending all of the support groups without appropriate need and thus is distracting his attention. They finally agree to split their time at different meetings and each then goes their separate ways.
During this time, Jack continues his car crash investigations by flying across the country, during which he meets Tyler Durden (BRAD PITT), a soap salesman with an interesting philosophy about life, not to mention part-time jobs where he splices pornographic images into family films as a projectionist or spikes served food with body fluids while working as a waiter.
Jack doesn't think much of Tyler until he returns home to find that his condo has blown up. Believing it to be an accident and without any real friends, he calls up Tyler and two get together for several rounds of beers. In the parking lot, Tyler urges Jack to hit him and after reluctantly doing so, the two get into a cathartic fight that changes Jack's life.
Soon Jack moves in with Tyler in his large, dilapidated home and their now weekly fist fights begin drawing crowds of onlookers and then participants. As such, they form a fight club where the rules are that only two men can spar at a given time and no one can mention the club outside their circle.
As Jack begins to accept Tyler's anarchistic philosophy about life and a lack of interest in his possessions or job, others, such as Angel Face (JARED LETO) do the same as well. With their numbers swelling and their activities decidedly becoming more antisocial, Jack begins to wonder if Tyler's going too far. Coupled with Marla now being Tyler's lover, Jack begins to feel more like an outsider and soon finds himself facing interesting and unexpected complications to his new lifestyle.