Plot

In late summer 1945, guests are gathered for the wedding of Don Vito Corleone's daughter Connie (Talia Shire) and Carlo Rizzi (Gianni Russo). Vito (Marlon Brando), the head of the Corleone Mafia family, is known as "Godfather." He and Tom Hagen (Robert Duvall), the Corleone family lawyer, are hearing requests for favors. One of the men is Amerigo Bonasera, an old friend of the Don, whose daughter was beaten by two young men who received minimal punishment. The Don's wife is godmother to Bonasera's shamed daughter, a relationship the Don uses to extract new loyalty from the undertaker. The Don agrees to have his men punish the young men responsible.

Meanwhile, the Don's youngest son Michael (Al Pacino), a decorated Marine hero returning from World War II service, arrives at the wedding and tells his girlfriend Kay Adams (Diane Keaton) about his father's criminal life; he reassures her that he doesn't plan to join them. Michael figuratively introduces the main characters to Kay. Fredo, Michael's next older brother, is mostly dimwitted. Sonny, the Don's eldest child, is married but a hot-tempered philanderer who sneaks into a bedroom with one of Connie's bridesmaids, Lucy Mancini. Tom Hagen is not related to the family by blood but is considered one of the Don's sons because he was homeless when he befriended Sonny in the Little Italy neighborhood of Manhattan. Now a talented attorney, Tom is being groomed for the important position of Consigliere (counselor) to the Don.

Also among the guests at the celebration is the famous singer Johnny Fontane (Al Martino), Corleone's godson, who has come from Hollywood to petition Vito's help in landing a movie role that will revitalize his flagging career. Jack Woltz (John Marley), the head of the studio, denies Fontane the part, but Don Corleone explains to Johnny: "I'm going to make him an offer he can't refuse." Hagen is dispatched to Los Angeles to meet with Woltz, but Woltz refuses. Fontane seduced and "ruined" a starlet that Woltz had a sexual relationship with. Woltz is persuaded otherwise, when he wakes up early the next morning and finds himself in a pool of blood with the severed head of his prized $600,000 stud horse, Khartoum.

The family meets with Virgil "The Turk" Sollozzo (Al Lettieri), who is being backed by the rival Tattaglia family. He asks Don Corleone for financing and political and legal protection for importing and distributing heroin. Despite the huge profit, Corleone refuses, explaining that his political influence would be jeopardized by a move into the narcotics trade. The Don's eldest son, hotheaded Sonny (James Caan), breaks rank during the meeting and questions Sollozzo's assurances as to the Corleone Family's investment being guaranteed by the Tattaglia Family. His father privately rebukes him later. Don Corleone then dispatches Luca Brasi to infiltrate Sollozzo's organization. During the meeting, while Brasi is bent over to allow Bruno Tattaglia to light his cigarette, he is stabbed in the hand by Sollozzo, and is subsequently garroted by an assassin.

Soon after his meeting with Sollozzo, Don Corleone is gunned down in an assassination attempt. Fredo Corleone had been assigned driving and protection duty for his father when Paulie Gatto, the Don's usual bodyguard, had called in sick. Fredo proves to be ineffectual. When Sonny hears about the Don being shot and Paulie's absence, he orders Clemenza to find Paulie and bring him to the Don's house. Sollozzo abducts Tom Hagen and persuades him to offer Sonny the deal previously offered to his father. Enraged, Sonny refuses to consider it and issues an ultimatum to the Tattaglias: turn over Sollozzo or face a lengthy, bloody and costly gang war. They refuse, and instead send Sonny "a Sicilian message," in the form of two fresh fish wrapped in Luca Brasi's bullet-proof vest, to tell the Corleones that Luca Brasi "sleeps with the fishes."

Clemenza later takes Paulie and one of the family's hit-men, Rocco Lampone, for a drive into Manhattan. Clemenza has Paulie stop the car in a remote area so he can urinate. Rocco shoots Paulie dead; he and Clemenza leave Paulie and the car behind. Michael, who is considered a "civilian" and not involved in mob business, visits his father. He is shocked to find that no one is guarding him. Realizing that his father is again being set up to be killed, he calls Sonny for help, moves his father to another room, and goes outside to watch the entrance. Michael enlists help from Enzo the baker (Gabriele Torrei), who has come to the hospital to pay his respects. Together, they bluff away Sollozzo's men as they drive by. Police cars soon appear bringing the corrupt Captain.

McCluskey, who breaks Michael's jaw when Michael insinuates that Sollozzo paid McCluskey to set up his father. Just then, Hagen arrives with "private detectives" licensed to carry guns to protect Don Corleone. Sonny responds by having Bruno Tattaglia, son and under-boss of Don Phillip Tattaglia, killed. Sollozzo requests a meeting with the Corleones, which Captain McCluskey will attend as Sollozzo's bodyguard. Michael offers to kill them both. Usually cops are off limits, but Michael says he is fair game as he is involved with Sollozzo. They meet in a restaurant where Michael is frisked, but he goes to the bathroom to recover his gun & shoots both.

Michael is sent to Sicily. Corleone family prepares for all-out warfare with the Five Families (who are united against the Corleones) as well as a general clampdown on the mob by the police and government authorities. Marriage between Connie and Carlo disintegrates as they argue over Carlo's suspected infidelity. One day, Sonny sees a bruise on Connie's face, and she tells him that Carlo hit her after she asked if he was having an affair. Sonny severely beats up Carlo Rizzi for brutalizing the pregnant Connie. An angry Carlo responds by plotting with Tattaglia and Don Emilio Barzini (Richard Conte), the Corleones' chief rivals, to have Sonny killed. Carlo again beats Connie in order to lure Sonny out in the open. When Connie phones the compound to tell Sonny that Carlo has beaten her again, the furious Sonny drives off (alone and not escorted) to fulfill his threat. On the way to Connie and Carlo's house, Sonny is ambushed at a highway toll booth and shot to death by several hit-men wielding Thompson sub-machine guns.

Don Corleone returns home from the hospital and is distraught to learn that it was Michael who killed Sollozzo and McCluskey and that Sonny is dead. Rather than seek revenge for Sonny's killing, Don Corleone meets with the heads of the Five Families to negotiate a cease-fire. Not only is the conflict draining all their assets and threatening their survival, but ending it is the only way that Michael can return home safely. Reversing his previous decision, Vito agrees that the Corleone family will provide political protection for Tattaglia's traffic in heroin, as long as it is controlled and not sold to children. At the meeting, Don Corleone deduces that Don Barzini, not Tattaglia, was ultimately behind the start of the mob war and Sonny's death.

In Sicily, Michael patiently waits out his exile, protected by Don Tommasino (Corrado Gaipa), an old family friend. Michael aimlessly wanders the countryside, accompanied by his ever-present bodyguards, Calo (Franco Citti) and Fabrizio (Angelo Infanti). In a small village, Michael meets and falls in love with Apollonia Vitelli (Simonetta Stefanelli), the beautiful young daughter of a bar owner. They court and marry in the traditional Sicilian fashion, but soon Michael's presence becomes known to Corleone enemies. As the couple is about to be moved to a safer location, Apollonia is killed when their car is bombed; Michael, who barely escapes alive, spots Fabrizio hurriedly leaving the grounds seconds before the explosion, implicating him in the assassination plot.

Michael returns home. More than a year later in 1950, he reunites with his former girlfriend Kay after a total of four years of separation -- three in Italy and one in America. He tells her he wants them to be married. Kay accepts his proposal. Michael is now in charge; he promises Kay he will make the family business completely legitimate within five years.

Two years later, Peter Clemenza (Richard S. Castellano) and Salvatore Tessio (Abe Vigoda), two Corleone Family capo-regimes (captains), complain that they are being pushed around by the Barzini Family and ask permission to strike back, but Michael denies the request. He plans to move the family operations to Nevada and after that, Clemenza and Tessio may break away to form their own families. Michael further promises Connie's husband, Carlo, that he will be his right-hand man in Nevada. Tom Hagen has been removed as Consigliere and is now merely the family's lawyer, with Vito serving as Consigliere. Privately, Hagen complains about his change in status, and also questions Michael about a new regime of "soldiers" secretly being built under Rocco Lampone (Tom Rosqui). Don Vito explains to Hagen that Michael is acting on his advice.

Another year or so later, Michael travels to Las Vegas and meets with Moe Greene (Alex Rocco), a rich and shrewd casino boss looking to expand his business dealings. After the Don's attempted assassination, Fredo had been sent to Las Vegas to learn about the casino business from Greene. Michael offers to buy out Greene but is rudely rebuffed. Greene believes the Corleones are weak and that he can secure a better deal from Barzini. As Moe and Michael heatedly negotiate, Fredo sides with Moe. Afterward, Michael warns Fredo to never again "take sides with anyone against the family."

Michael returns home. In a private moment, Vito explains his expectation that the Family's enemies will attempt to murder Michael by using a trusted associate to arrange a meeting as a pretext for assassination. Vito also reveals that he had never really intended a life of crime for Michael, hoping that his youngest son would hold legitimate power as a senator or governor. Some months later, Vito collapses and dies. At the burial, Tessio conveys a proposal for a meeting with Barzini, which identifies Tessio as the traitor that Vito was expecting.

Michael arranges for a series of murders to occur simultaneously while he is standing godfather to Connie's and Carlo's newborn son at the church: Don Stracci (Don Costello) is gunned down along with his bodyguard in a hotel elevator by Clemenza. Moe Greene is killed while having a massage, shot through the eye by an unidentified assassin. Don Cuneo (Rudy Bond) is trapped in a revolving door and shot dead by soldier Willi Cicci (Joe Spinell). Don Tattaglia is assassinated in his bed, along with a prostitute, by Rocco Lampone and an unknown associate. Don Barzini is killed on the steps of his office building along with his bodyguard and driver, shot by Al Neri (Richard Bright), disguised in his old police uniform. After the baptism, Tessio believes he and Hagen are on their way to the meeting between Michael and Barzini that he has arranged. Instead, he is surrounded by Willi Cicci and other button men as Hagen steps away. Realizing that Michael has uncovered his betrayal. Meanwhile, Michael confronts Carlo about Sonny's murder and forces him to admit his role in setting up the ambush, having been approached by Barzini himself. Michael assures Carlo he will not be killed, but his punishment is exclusion from all family business. He hands Carlo a plane ticket to exile in Las Vegas. However, when Carlo gets into a car headed for the airport, he is garroted to death by Clemenza, on Michael's orders.

Later, a hysterical Connie confronts Michael at the Corleone compound as movers carry away the furniture in preparation for the family move to Nevada. She accuses him of murdering Carlo in retribution for Carlo's brutal treatment of her and for his suspected involvement in Sonny's murder. After Connie is removed from the house, Kay questions Michael about Connie's accusation, but he refuses to answer, reminding her to never ask him about his business or what he does for a living. She insists, and Michael outright lies, reassuring his wife that he played no role in Carlo's death. Kay believes him and is relieved. The film ends with Clemenza and new capo-regimes Rocco Lampone and Al Neri arriving and paying their respects to Michael. Clemenza kisses Michael's hand and greets him as "Don Corleone." As Kay watches, the office door is closed. Michael is the new Godfather.