On a road trip through the South, New Yorkers Bill Gambini and his friend, Stan Rothenstein, stop at a convenience store called the Sac-O-Suds in Beechum County, Alabama, where they buy groceries, then drive away. Bill realizes he failed to pay for a can of tuna just as a police car pulls them over. Bill and Stan are arrested. Assuming he is being charged with petty theft, Bill confesses guilt at the police station. Sheriff Farley reveals that he is being charged with the murder of the Sac-O-Suds clerk, Jimmy Willis, and Stan is being charged as an accessory. The young men panic. They are allowed to make phone calls, but Stan cannot reach his parents, who are travelling in Chile. Bill calls his mother and tells her he needs a good attorney. She cannot afford to pay an expensive lawyer, but informs him that his cousin, Vincent “Vinny” LaGuardia Gambini, has become an attorney. Soon, Vinny Gambini and his fiancée, Mona Lisa Vito, arrive in town. With their flashy clothes and thick New York accents, they seem out of place. When he visits them in jail, Bill and Stan are discouraged to learn that Vinny has only six weeks’ experience as a personal injury attorney, after spending six years trying to pass the New York bar exam. Futhermore, he has no courtroom experience. Vinny meets with Judge Chamberlain Haller, who must approve all out-of-state attorneys. Vinny lies that he has been practicing law for sixteen years and has had several murder cases. Haller gives him a book on Alabama Rules of Criminal Procedure, and warns that Vinny will not receive special treatment in his courtroom. Mona Lisa and Vinny settle into a motel room. At dawn, they are awakened by a steam whistle. They go to a diner, where Vinny reluctantly eats grits for the first time in his life. He goes to the courthouse for Bill and Stan’s arraignment. Judge Haller reprimands Vinny for failing to stand up when addressing the court, and for dressing too casually in a leather jacket. Haller asks Vinny several times how his clients plead, but Vinny argues their innocence instead of answering “guilty” or “not guilty.” Haller holds Vinny in contempt of court, and he is arrested. Mona Lisa pays his $200 bail and picks him up at the jail, where a crowd of protestors picket the upcoming execution of a prisoner. Mona Lisa worries that Vinny’s cousin Bill could be sentenced to death if found guilty, and criticizes Vinny’s performance at the arraignment. Meanwhile, Stan expresses concern that Vinny is incompetent, but Bill is unwilling to fire his cousin. He believes Vinny will improve, and promises his friend that the Gambinis live to argue. At a preliminary hearing, Vinny fails to wear a suit and is again found guilty of contempt of court. Hoping to get a good night’s sleep, Mona Lisa and Vinny check into a new hotel, where they are awakened by the sound of hogs at a nearby market. Vinny meets with Bill, who confesses that he and Stan have hired public defender John Gibbons. Vinny talks Bill into changing his mind, but Stan retains Gibbons as his attorney. Jim Trotter, III, the district attorney prosecuting Bill and Stan, invites Vinny to go hunting. Vinny asks Trotter for copies of his files, and, when Trotter agrees, he returns to his hotel room triumphant. Mona Lisa, who has repeatedly offered support to Vinny and has been reading his book on Alabama court procedure, informs her fiancé that Trotter has to share his files by law. Fed up with Vinny’s inadequacy, Mona Lisa reminds him of his promise to marry her after he wins his first court case. She has been waiting ten years, and claims her “biological clock is ticking.” The bickering couple spends the night at a cabin, hoping for peace and quiet. However, they are frightened by noises in the middle of the night and end up sleeping in Jimmy’s car during a rainstorm. After another sleepless night, Jimmy ruins his new suit while trying to free his car from the mud. With only an hour before Bill and Stan’s trial begins, he is forced to buy a red velvet tuxedo from a second-hand store. Haller accuses Vinny of mocking him when he arrives late in the ridiculous clothing, and holds him in contempt of court yet again. An exhausted Vinny falls asleep during Jim Trotter’s opening statement. When it is his turn to speak, Vinny tells the jury that everything Trotter said is “bullshit,” and sits back down. Stan’s attorney, John Gibbons, stutters his way through an opening statement, and apologizes for being nervous. The first witness, Sam Tipton, is called to the stand. Tipton claims he saw Bill and Stan enter the Sac-O-Suds from his home. He proceeded to cook grits from scratch, and five minutes later, sat down to eat breakfast as Bill and Stan fled the Sac-O-Suds. With his newfound knowledge of grits and how they are prepared, Vinny catches Tipton in a lie, arguing that only instant grits could have been made in five minutes. Stan’s faith in Vinny is restored, and he re-hires him. Having been arrested a third time for contempt of court, Vinny tells Mona Lisa not to bail him out so he can have a night of sleep in jail. However, a blaring alarm bell wakes him up too early. When court re-convenes, Vinny questions an aged witness named Constance Riley, who claims she saw the defendants when they were fifty feet away from her. Vinny holds up fingers in back of the courtroom to prove that Constance cannot see clearly from that distance. Expert witness George Wilbur testifies that tire marks left in the Sac-O-Suds parking lot match the tires on Bill’s mint-green 1964 Buick Skylark. During a lunch break, Mona Lisa offers to help Vinny go over new evidence. She provides a stack of photographs she snapped on their trip, but Vinny dismisses them. Mona Lisa leaves in a huff. Vinny takes another look at her snapshots and realizes something. He calls her to the stand as an expert in the field of automobiles. Jim Trotter questions her expertise, but Mona Lisa, who comes from a family of mechanics, proves her knowledge by answering his questions. Vinny presents her with a picture she took of the tire tracks at the Sac-O-Suds. She examines the picture and sees the same thing he just discovered – the tire tracks are in a solid line, equally far apart, as they go over a median. Mona Lisa deduces the tracks must have been made by a 1963 Pontiac Tempest, the only car resembling a Buick Skylark with “positraction,” a limited slip differential, and the independent rear suspension necessary to make those marks. Vinny calls George Wilbur back to the stand, and he attests to Mona Lisa’s accuracy. Sheriff Farley runs a search for stolen or abandoned 1963 Tempests, and finds a report of two men driving such a car who were recently arrested in Georgia, and in possession of the same type of gun that killed Jimmy Willis. Trotter dismisses charges, and the case is thrown out. After parting ways with a jubilant Bill and Stan, Vinny and Mona Lisa drive back to New York and bicker about their upcoming wedding.