In 1950s Philadelphia, Sheeran works as a delivery truck driver and starts to sell some of the contents of his shipments to local gangster Felix "Skinny Razor" DiTullio. After his company accuses him of theft, union lawyer Bill Bufalino gets him off after Sheeran refuses to name his customers to the judge. Bill introduces Sheeran to his cousin Russell Bufalino, head of the Northeastern Pennsylvania crime family. Sheeran begins to do jobs for Russell and members of the local South Philadelphia underworld, including "painting houses," a euphemism for murder. Soon, Russell introduces Sheeran to Jimmy Hoffa, head of the International Brotherhood of Teamsters, who has financial ties with the Bufalino crime family and is struggling to deal with fellow rising Teamster Anthony "Tony Pro" Provenzano, as well as mounting pressure from the federal government. Hoffa becomes close with Sheeran and his family, especially his daughter Peggy, and Sheeran becomes Hoffa's chief bodyguard while on the road.
After the 1960 election of John F. Kennedy, Russell is thrilled while Hoffa is livid. Sheeran would later help deliver weapons for the CIA in their failed attempt to overthrow the Cuban government. Kennedy's brother, Robert F. Kennedy, who was named Attorney General, forms a "Get Hoffa" squad in an effort to bring down Hoffa, who is eventually arrested and convicted in 1964 for jury tampering.
While Hoffa is in prison, his replacement atop the Teamsters, Frank Fitzsimmons, begins overspending the labor union's pension fund and making interest-free loans to the Mafia. Hoffa's relationship with Provenzano, himself arrested for extortion, also deteriorates beyond repair. Hoffa has his sentence commuted by President Richard Nixon in 1971, although he is forbidden from partaking in any Teamsters activities until 1980.
Despite his parole terms, Hoffa undertakes a plan to reclaim his power atop the organized unions. Hoffa's growing disrespect for other Teamster leaders and related crime family interests begins to worry Russell. During a dinner in Sheeran's honor in October 1973, Russell tells Sheeran to confront Hoffa and warn him that the heads of the crime families are displeased with his behavior. Hoffa then informs Sheeran that he "knows things" that Russell and the other dons are unaware that he knows, and further claims that he is untouchable, for if anything ever happened to him they would all end up in prison.
In 1975, while on their way to the wedding of Bill's daughter, Russell tells Sheeran that the dons have become fed up with Hoffa and have sanctioned his murder. Reluctantly, Russell informs Sheeran that he has been chosen as the triggerman, fearing he might otherwise try to warn or save Hoffa. The two drive to an airport where Sheeran boards a plane to Detroit. Sheeran tells Hoffa he will be in town early in the day but arrives late that afternoon. Hoffa, who had scheduled a meeting at a local diner with Provenzano and Anthony Giacalone, is surprised to see Sheeran arrive with Hoffa's unsuspecting foster son Chuckie O'Brien and gangster Sal "Sally Bugs" Briguglio.
They advise Hoffa that the meeting was moved to a house where Provenzano and Russell would be waiting for them; Sheeran reassures Hoffa that everything is fine and he joins them in the car. Entering the house, Hoffa finds it empty and realizes that he has been set up. He turns around to leave at which point Sheeran shoots him twice at point-blank range before leaving the gun atop his body near the entrance. After Sheeran departs, two younger gangsters have the body cremated to eliminate all traces of him.
After taking the Fifth in a grand jury investigation into Hoffa's disappearance, Sheeran, Russell, Provenzano and others are eventually convicted on various charges unrelated to Hoffa's murder. One by one, the now elderly gangsters begin to die in prison. Sheeran is eventually released and placed in a nursing home. He tries to reconcile with his alienated daughters, but Peggy, suspecting he had involvement in Hoffa's disappearance, severs all contact with him. Sheeran begins a friendship with a Catholic priest assigned to the nursing home who gives Sheeran absolution for crimes committed over his lifetime. As the priest leaves, Sheeran asks him to leave the door slightly ajar, emulating one of Hoffa's habits.
- Robert De Niro as Frank "The Irishman" Sheeran
- Al Pacino as Jimmy Hoffa
- Joe Pesci as Russell Bufalino
- Anna Paquin as Peggy Sheeran
- Bobby Cannavale as Felix "Skinny Razor" DiTullio
- Harvey Keitel as Angelo Bruno
- Ray Romano as Bill Bufalino
- Albert Cobrovsky as "Mobster"
- This is third film in which Al Pacino and Robert De Niro appeared on-screen together. The first two films are Heat and Righteous Kill. They both starred in The Godfather Part II but never appeared on screen together.
- This is the first Martin Scorsese film since Casino to star Robert De Niro and Joe Pesci.
To be added