In 1955, a young Henry Hill becomes enamored of the criminal life and Mafia presence in his working class Italian-American neighborhood in Brooklyn. He begins working for local caporegime Paul "Paulie" Cicero and his associates: James "Jimmy" Conway, an Irish truck hijacker and gangster, and Tommy DeVito, a fellow juvenile delinquent. Henry begins as a fence for Jimmy, gradually working his way up to more serious crimes. The three associates spend most of their nights in the 1960s at the Copacabana nightclub carousing with women. Henry starts dating Karen Friedman, a Jewish woman. She is initially troubled by Henry's criminal activities but is eventually seduced by his glamorous lifestyle. She marries him, despite her parents' disapproval.
In 1970, Billy Batts, a made man in the Gambino crew who was recently released from prison, repeatedly insults Tommy at a nightclub owned by Henry; Tommy and Jimmy then beat, stab and shoot him to death. The unsanctioned murder of a made man invites retribution; realizing this, Jimmy, Henry, and Tommy cover up the murder by burying the body in Upstate New York. Six months later, however, Jimmy learns that the burial site is slated for development, prompting them to exhume and relocate the decomposing corpse.
In 1974, Karen harasses Henry's mistress Janice and holds Henry at gunpoint. Henry moves in with Janice, but Paulie insists that he should return to Karen after collecting a debt from a gambler in Tampa with Jimmy. Upon returning, Jimmy and Henry are arrested after being turned in by the gambler's sister, an FBI typist, and they receive ten-year prison sentences. In order to support his family on the outside, Henry has drugs smuggled in by Karen and sells them to a fellow inmate from Pittsburgh. In 1978, Henry is paroled and expands this cocaine business against Paulie's orders, soon involving Jimmy and Tommy.
Jimmy organizes a crew to raid the Lufthansa vault at the JFK Airport, stealing several millions in cash and jewelry. After some members purchase expensive items against Jimmy's orders and the getaway truck is found by police, he has most of the crew murdered. In his voiceover narration, as dead bodies are being discovered all over the city, Henry theorizes that Jimmy would have killed them anyway rather than share the profits of the heist. Tommy and Henry are spared by Jimmy. Tommy, however, is later led to believe that he is to become a made man, but is ultimately shot dead on the way to the ceremony in retribution for Batts' murder.
By 1980, Henry has become a nervous wreck from cocaine use and insomnia. He sets up a drug deal with his Pittsburgh associates, but is arrested by narcotics agents, and jailed. After bailing him out, Karen explains that she flushed $60,000 worth of cocaine down the toilet to prevent FBI agents from finding it during their raid, leaving them virtually penniless. Feeling betrayed by Henry's drug dealing, Paulie gives him $3,200 and ends their association. Henry meets Jimmy at a diner and is asked to travel on a hit assignment, but the novelty of such a request makes him suspicious. Henry realizes that Jimmy plans to have him and Karen killed, prompting his decision to become an informant and enroll, with his family, in the witness protection program. He gives sufficient testimony to have Paulie and Jimmy arrested and convicted. Henry is grateful to be alive, but he is forced out of his gangster life and has to readjust to normal life once again; he narrates, "I'm an average nobody. I get to live the rest of my life like a schnook."
The end title cards state that Henry is still a protected witness as of 1990, but that he was arrested in 1987 in Seattle for narcotics conspiracy, receiving five years' probation. He has been clean since then. He and Karen separated in 1989 after 25 years of marriage, while Paulie died the previous year in Fort Worth Federal Prison at age 73 from respiratory illness. Jimmy is serving a 20 years to life sentence in a New York prison for murder, in which he will be paroled in 2004, when he will be 78 years old.