In the 1800s, in Arizona, a reformed gunfighter, who is hiding behind the alias “Johnny Guitar,” shows up at an out-of-the-way gambling casino located in an unlikely spot near a sleepy town. The owner, the steely, opportunistic Vienna, built the casino there in anticipation of the construction of a transcontinental railroad and has promised to share her hoped-for fortune with her four loyal employees, Eddie, Frank, Sam and Old Tom. Shortly after Johnny arrives, several vigilante ranchers, led by the venomous Emma Small, ride up and accuse Vienna of being part of a gang that robbed the stagecoach and killed her brother, the town's banker. Although Jenks, the stagecoach driver, is unable to identify the four masked gunmen who held him up, Emma, who did not witness the crime, insists the gang led by the Dancin’ Kid, who is Vienna's occasional lover, is reponsible. Because Vienna remains close-mouthed about the Kid and the ranchers feel threatened by the coming of the railroad and Vienna's profiting from it, they are easily roused into greater antagonism against Vienna by Emma’s tirades. After tricking the jealous Emma into revealing her unrequited passion for the Kid and her need for irrational revenge, Vienna boldly stands her ground, until the neurotic Emma vows to kill her. The approach of the Kid and his men escalates the tension, which Johnny tries to break by playing the guitar. The Kid grabs Emma for a dance, but Marshal Williams interrupts to question him about the robbery, refusing to believe that the gang has been mining a secret silver lode, as they claim. Williams gives Vienna twenty-four hours to close up and leave town, but Vienna refuses to be forced out and Johnny pledges to assist her, making the Kid jealous. One of his men, Bart Lonergan, picks a fight with the unarmed Johnny, who nevertheless beats the ruffian in a fistfight. After the establishment clears for the night, Vienna discusses her business plans with Johnny, who is an old flame she has secretly asked to help her. Although they broke up five years before, Johnny wants to revive their relationship. However, Vienna claims that the intervening years have taught her not to love and points out the inequities of gender, which allow a man to lie, steal, kill and retain his pride, while labeling a woman a tramp after one slip. The next day in their mountain hideout, the Kid and his gang wonder which of the many outlaw gangs in the area might have robbed the stagecoach. As their mine has petered out, they are anxious to move to California, and reproach the Kid for hanging around because of Vienna. The Kid counters that he hates to run away from something he did not do, but decides to finance their move by robbing the local bank, as they have already been condemned by the town. Meanwhile, Vienna has decided to pay off her employees, including Johnny, and send them away to safety, until the tension in the town dies down. When she goes to the bank to withdraw funds, the Kid’s gang shows up and robs it, drawing more suspicion on her. A posse quickly forms, which Emma insists on joining, and they pursue the gang, whose escape is complicated by the dynamiting of the pass by railroad workers. In the chase, the teenaged Turkey Ralston, the youngest member of the Kid’s gang, is injured and left behind and, having nowhere else to go, makes his way to Vienna, with whom he is smitten. Old Tom, who has remained behind out of loyalty to Vienna, tries to hide him in the woods, but the posse, urged by Emma, detours there. Although Vienna quickly tries to conceal him, Turkey is soon found. John McIvers, a prosperous rancher in sympathy with Emma, promises Turkey that, if he will confess to Vienna’s participation in the gang, they will not hang him. Turkey is reluctant to accuse Vienna falsely, but she tells him to save himself. However, after he tells the posse what they want to hear, McIvers reneges on his promise and the posse, again aroused by Emma’s incessant fuming, prepares to hang both Turkey and Vienna. In the following struggle, Williams and Old Tom are shot, and the crazed Emma gleefully sets fire to the building. After Turkey is hanged, none of the men are willing to hang Vienna, even for Emma’s generous bribe. Emma attempts the task, but Johnny frees Vienna, and the former lovers hide in the cellar of the burning building. Through a connecting mine shaft, they escape, and the next day show up at the Kid’s lair, where they form an uneasy alliance with the gang. However, Turkey’s horse soon leads the posse to their hiding place, and Bart betrays his cohorts. As the posse nears, gun fighting commences and most of the gang is killed. Soon, realizing that the fight is really between Vienna and the irrational Emma, the posse loses interest. In a final showdown, Emma and Vienna shoot it out, and Emma is killed. The posse takes the captured Kid and Emma’s body down the mountain, followed by Johnny and Vienna, who are now reunited and free.