Navin R. Johnson, a homeless man, directly addresses the camera and tells his story. He is the adopted white son of African American sharecroppers, who grows to adulthood naïvely unaware of his obvious adoption. He stands out in his family not just because of his skin color but because of his utter lack of rhythm when his adopted family plays spirited blues music. One night, he hears the staid Roger Wolfe Kahn Orchestra song called "Crazy Rhythm" on the radio and his feet spontaneously begin to move with the urge to dance; he sees this as a calling and decides to hitchhike to St. Louis, from where the song was broadcast. On the way, he stops at a motel, where a dog wakes him up by barking at his door. Navin thinks the dog is trying to warn of a fire. He wakes up the other hotel guests to rescue them, but everyone realizes it was a false alarm.
Navin gets a job (and a place to sleep) at a gas station owned by Mr. Harry Hartounian. He is thrilled to find that he is listed in the local phone book, as his name is "in print" for the first time. Not long after, a gun-wielding lunatic randomly flips through the phone book and picks "Johnson, Navin R." as his next victim. As the madman watches through his rifle scope, waiting for a clear shot, Navin fixes the slippery glasses of a customer, Stan Fox, by adding a handle and a nose brake. Fox offers to split the profits 50/50 with Navin if he can market the invention, then departs. Seizing his chance, the crazed sniper shoots but misses. The lunatic chases Navin to a traveling carnival, where Navin hides out, eventually getting a job with SJM Fiesta Shows as a weight guesser. While employed there, Navin meets an intimidating daredevil biker named Patty Bernstein and has a sexual relationship with her, finally realizing what his "special purpose" (his mother's euphemism for his penis) is for. He then meets a woman named Marie and arranges a date with her. Patty confronts them, but Marie knocks her out. While courting, Navin and Marie walk along the beach and sing "Tonight You Belong to Me"; Navin plays the ukulele and Marie the cornet. Navin and Marie fall in love, but Marie reluctantly leaves him because of his lack of financial security. She writes a note and slips out while Navin is in the bath.
At an emotional and financial low, Navin is soon contacted by Stan Fox with exciting news: his glasses invention, now called the Opti-Grab, is selling big and he is entitled to half of the profits. Now extremely rich, he finds and marries Marie, and they buy an extravagant mansion. Their life becomes one of splendor and non-stop partying. However, a motion-picture director (Carl Reiner, playing himself) files a class action lawsuit against Navin. Reiner claims that the Opti-Grab caused his eyes to be crossed and his resulting poor vision caused the death of a stunt driver in the film he was directing. Nearly ten million other people have the same vision complaint (including the judge and jury foreman), and are awarded $10 million in damages. Bankrupt, depressed, and now homeless, he is abandoned by Marie and is soon living on the streets. His story now told, he resigns himself to a life of misery and memories of Marie, but to his amazed joy, she suddenly appears, along with Navin's family, and some more good news: having carefully invested the small sums of money he sent home throughout the film, they have become wealthy themselves. They pick him up off the street, and he and Marie move back home into the Johnsons' new house — a much larger but identical version of their old, small shack.
The story ends as the entire family dances on the porch and sings "Pick a Bale of Cotton"; Navin dances along, now having gained perfect rhythm.
By 1977, comedian Steve Martin was experiencing wild success. He wished to cross over to a film career, believing it promised more longevity. Basing his film proposal on a line from his act — "It wasn't always easy for me; I was born a poor black child" — he fleshed out his ideas into a series of notes he intended to deliver to studios. With confidence in his budding standup career, he imagined it would not be difficult to break into Hollywood. Instead, he found it more difficult than expected. Bill McEuen was acquainted with Paramount Pictures president David Picker, and passed along his notes, which the studio read carefully. It described a series of odd jobs lead character "Steve" would hold in his saga, but Paramount passed on the project. Picker moved to Universal Studios around this time, and moved the film along with him. Martin was able to pick which director he wanted to work with, and chose Carl Reiner, famous for his work on The Dick Van Dyke Show. The duo met constantly, and the film's title grew out of their conversations: "It needs to be something short, yet have the feeling of an epic tale," Martin remarked. "Like Dostoyevsky's The Idiot, but not that. Like The Jerk."
Martin wrote the part of "Marie" with Bernadette Peters in mind. He adapted several bits of his standup act to fit within the film, such as a monologue in which he emotionally exits a scene, remarking "I don't need anything," but nevertheless picking up each object he passes on his way out. In co-writing the script with Carl Gottlieb and Michael Elias, their goal was to provide a laugh on each page of the screenplay. In shooting the film, Reiner "ran a joyful set", according to Martin, with the cast and crew eating lunch together each day. Martin's favorite moment of the film, as he detailed in his 2007 memoir Born Standing Up, was the scene in which he and Peters sing "Tonight You Belong to Me". Martin felt the moment was touching, and waited in anticipation at the film's premiere screening in St. Louis. Unfortunately, much of the audience left during the scene to buy more popcorn.
There was a scene in which Bill Murray was to have made a cameo but it was cut from the final film.
An alternate, comic introduction of Marie (Peters) – near the train ride Navin was running at the carnival – was only in the theatrical version and thus edited out in future versions. When her nephew takes off on the train, Navin rescues him, and in returning the boy to Marie, has the bill of his engineer's cap pulled down over his eyes so he cannot see the toy village he (Navin) destroys . . This scene may have been edited due to a reference to Godzilla.
A box office smash earning over $73 million (making the movie the eighth highest-grossing of 1979) and produced on a modestly low budget of $4 million. It has an 84% approval rating on Rotten Tomatoes. The website IGN ranked the film as the 10th top comedy film of all time.
The New York Times reviewer wrote that The Jerk "is by turns funny, vulgar and backhandedly clever, never more so than when it aspires to absolute stupidity. And Mr. Martin, who began his career with an arrow stuck through his head, has since developed a real genius for playing dumb ... Even when it's crude — which is quite a lot of the time — it's not mean-spirited ... Mr. Martin and his co-star, Bernadette Peters, work very sweetly together, even when they sing a duet of 'Tonight You Belong to Me,' carrying sweetness to what could easily have become an intolerable extreme."
The Jerk has been praised as not only one of Martin's best comedic efforts, but also one of the funniest films ever made. In 2000, readers of Total Film magazine voted The Jerk the 48th greatest comedy film of all time. This film is No. 20 on Bravo's 100 Funniest Movies and No. 89 on the American Film Institute list AFI's 100 Years...100 Laughs. Premiere magazine voted Steve Martin's performance of Navin Johnson No. 99 on their list, "The 100 Greatest Performances of All Time". A BBC poll of more than 250 critics rated the film as the 99th greatest comedy of all time.
The Jerk had a 1984 television film sequel, The Jerk, Too, starring Mark Blankfield as Navin and co-starring Stacey Nelkin. It was produced, but not written, by Steve Martin.