Our film begins in the mid-1940’s. New York City crime boss, Vito Corleone, is celebrating his daughter’s wedding day, by acting in his role as the Godfather to his guests, and deciding which requests to grant, and which requests to deny.
The wedding is attended by many elements of the New York underworld, as well as the entire Corleone family, including Vito’s godson, the famous singer Johnny Fontane, Vito’s United States Marine son, Michael, and Michael’s new girlfriend Kay. The wedding is a huge success, and the back room deals are struck. Michael tells Kay at the wedding some of the dirty family history, and tells her that is his family and not him, assuring her that he wants no part of his father’s criminal enterprise.
The film switches to Hollywood where the Don’s consigliore, Tom Hagen, has been dispatched to strike a deal with film studio head Jack Woltz on behalf of Johnny Fontane. Fontane needs a role in an upcoming film to reignite his failing career. Unfortunately, Woltz is hell bent on destroying Fontane due to the singer messing around with a starlet that the lecherous studio head had his eye on. Woltz denies Don Corleone’s request for a favor, but little did the filmmaker know that it was an offer that he couldn’t refuse. Woltz soon wakes up with his prize horse’s decapitated head in his bed. The message is sent, and Fontane soon gets the role.
The film then shifts to Christmastime, 1945. A drug peddler on the rise known as The Turk wishes to meet with Don Corleone to make his argument for the Don to invest in his criminal enterprise and provide protection. However, Vito disapproves of the drug trade and rejects the offer. Unfortunately, Sonny, Vito’s eldest son, gives a subtle hint that he is interested in the deal when he speaks out of turn in front of the Turk. Feeling that there is an opportunity for a deal if the Don is out of the picture, the Turk attempts to assassinate Vito.
Don Corleone is shot several times but survives. With the Don now in the hospital, Sonny takes control of the family, and launches into a full scale gang war. Michael returns home to help, abandoning his reservations about becoming involved in the family business. After preventing a second hit on his father at the hospital, Michael volunteers for, and successfully completes the plan to murder the Turk and a dirty police captain that is in the Turk’s employ. Michael is then sent off to Italy in secret to avoid the law and the fallout of his own dirty deals.
While Michael is in Italy, the Five Families erupt in open warfare, and the family business takes a major hit. Sonny sends his other brother, Fredo, to Las Vegas for shelter, and to learn the casino business from Moe Greene. At the same time, Sonny deals with more personal matters at home when his brother in law beats his sister, Connie. Fiery tempered Sonny brutally attacks his brother in law Carlo in the street, threatening to kill him if he ever touched his sister again.
Meanwhile, in Italy, Michael has fallen in love with local girl, Apollonia, and marries her. But back at home, Carlo has beaten Connie again, and Sonny leaves the safety of the Corleone compound, and is brutally gunned down by submachine gun fire at a highway toll booth. When news of Sonny’s death reaches Italy, Michael’s protector feels that Michael and Apollonia are in danger and wants to move them. Unfortunately, it is too little too late, as Apollonia is killed by a car bomb meant for Michael and planted by one of Michael’s bodyguards.
Devastated by Sonny’s death, Vito decides to end the gang war. Believing that the Tattaglias were secretly under orders of Don Barzini, he promises, before the heads of the Five Families, to withdraw his opposition to their heroin business, and forgo revenge for Sonny’s murder. His safety guaranteed Michael returns home to a father saddened by his involvement in the family business, and Michael marries Kay the next year.
Upon his return, Michael assumes command of the family, with his father now content to merely advise his youngest son. Michael promises Kay that he will make the business legitimate within five years. To that end, Michael insists Hagen relocate to Las Vegas, and relinquish his role to Vito. Tom is hurt by the demotion but Michael and Vito explain that Tom is not a “wartime consigliore” and that Tom should have no part in what will happen in the coming battles with rival families. When Michael travels to Las Vegas to buy out Greene’s stake in the family’s casinos, Greene derides the Corleones as a fading power. To add injury to insult, Michael sees Fredo falling under Greene’s sway.
Vito collapses and dies in his garden while playing with Michael’s son, Anthony. At the funeral, Vito’s trusted lieutenant Salvatore Tessio arranges a meeting between Michael and Don Barzini, signaling to Michael the treachery that Vito had previously warned of. The meeting is set for the same day as the christening of Connie’s son, to whom Michael will stand as godfather. The film shows as the christening proceeds, Corleone assassins, acting on Michael’s orders, murder the other New York dons and Moe Greene. At the same time, Tessio is told by Tom that Michael is aware of his betrayal and taken off to his death.
Michael personally questions his brother in law Carlo about his involvement in setting up Sonny’s murder. After initially denying any involvement, Carlo confesses he was contacted by Barzini. After Michael tells Carlo that he is out of the family business, Clemenza kills Michael’s brother in law. Later, Michael is confronted by Connie, who accuses him of having her husband killed. He denies killing Carlo when questioned by Kay, an answer she accepts. Then Kay watches with apprehension as Michael receives his capos, who address him as the new Don Corleone.