Curly Bill Brocuis (Powers Boothe) and his band of Cowboys slaughter innocent people at a wedding. Wyatt Earp (Kurt Russell) and his brothers Virgil (Sam Elliot) and Morgan (Bill Paxton) arrive in Tombstone, Arizona. The men hope to settle down with their wives and start a new life, this time without having to keep the law. When Wyatt Earp arrives, he meets long time friend and partner Doc Holliday (Val Kilmer). The two start talking about their past travels, and it is implied that Holliday is dying of tuberculosis. Holliday tells Earp that a group of vicious outlaw Cowboys run Tombstone. Earp goes home to a wife addicted to a laudanum, a common drug of the time mixing morphine and opium. Earp begins an affair with a traveling actress named Josephine Marcus.
The Tombstone town marshal is killed by a Cowboy. An angry mob wants to lynch the murderer, but Earp steps in and prevents the man from being killed. Virgil, who feels sorry for the people of the town, agrees to take the position of town marshal. Virgil instates a new law that no men are allowed to carry weapons into town, and all weapons must be checked in on the outskirts of town. This law maintains peace in Tombstone for a while, but eventually Brocius and his gang come riding into town, completely armed. Virgil, Wyatt, Morgan, and Doc Holliday decide to confront the Cowboys and try and get them to give up their weapons. They confront the Cowboys at the OK Corral, and they tell the men of their intentions to arrest them. The men resist, and a shootout breaks out. The lawmen kill many Cowboys, but one by the name of Ike Clanton escapes and tells the other Cowboys the news.
Later, the Cowboys ambush first Virgil, maiming him with a shogun blast to the back. They then creep up on Morgan who is playing billiards and fatally shoot him through the window of a door. Wyatt decides that the best thing for them and the people of the town would be for them to leave town. On the way out of town, they are ambushed once again by the Cowboys. Wyatt returns to Tombstone and vows to kill every last Cowboy. They track down and kill a number of Cowboys, shooting and hanging them.
Wyatt is confronted by Johnny Ringo, a gunslinger and member of the Cowboys. Ringo challenges Earp to a duel. Wyatt accepts, but he and Doc Holliday both know that Ringo is a much faster gunfighter than Wyatt. In the next scene we see Ringo waiting for Earp to show up. Doc Holliday volunteers to take on Ringo and shows up ahead of Wyatt. Ringo isn't happy to face Doc who shoots Ringo. Wyatt arrives late to find that Doc has taken his kill. The lawmen leave Arizona and every character goes his separate way. Virgil goes to California to become sheriff of a small town. Doc goes to a hospital to spend the remainder of his days, where he is visited frequently by Wyatt Earp. Finally, Wyatt Earp is shown settling down with Josephine Marcus, and living out the remainder of his days in peace.