Tensions rise between rival gangs the Jets (white) and the Sharks (Puerto Rican) as they struggle for control of the streets of New York City. In order to assert their dominance, Jets leader Riff plans to set up a rumble with the Sharks. He convinces a reluctant Tony, friend and former member, to join them, though Tony dreams of a better future away from gang life.
Everyone convenes at the neighborhood dance and its love at first sight for Tony and Maria, who has recently arrived from Puerto Rico and is soon to be wed to Chino, a member of the Sharks. They dance, fall in love, and try to kiss but Maria’s brother (and leader of the Sharks) Bernardo pulls her away. Later that night, Tony serenades Maria on the fire escape of her building and the two profess their love for one another. The Jets and the Sharks meet on neutral ground at Doc’s, a drugstore, and the leaders agree to no weapons at the fight.
The next day, Maria learns of the rumble and begs Tony to stop it, to which he agrees. However, when he arrives, the fight has already begun. When he tries to intervene, Bernardo pushes him down. Riff punches Bernardo in Tony’s defense and they both draw switchblades. Riff has an opportunity to stab Bernardo, but Tony holds him back. Riff returns to the fight but is accidentally stabbed and killed by Bernardo in the process. In a fit of rage, Tony grabs Riff’s knife and kills Bernardo. Sirens approach and the gangs disperse. Tony stands over Riff and Bernardo until hopeful tomboy Anybodys tells him to flee the scene.
Blissfully unaware of what has happened, Maria daydreams about Tony on the rooftop until Chino brings her the news. Tony arrives to see Maria and she is outraged, but she still loves him and they plan to run away together. Though Bernardo’s girlfriend Anita is angry with Tony, she finally realizes Maria loves him as much as she loved Bernardo and she reveals to them that Chino has a gun and is looking for Tony.
The police arrive to question Maria about her brother’s death. Anita races to Doc’s to tell Tony to wait for Maria, and instead finds the Jets who begin taunting and attacking her. After Doc arrives and stops them, a furious Anita spitefully delivers the wrong message, telling them that Chino has shot Maria dead. Learning the news of his beloved’s death, Tony begs Chino to kill him, too. Just as Tony sees Maria alive, Chino pulls the trigger. An enraged Maria grabs the gun but is unable to bring herself to fire it. She tells everyone that they all killed Tony because of their hate for each other. Gradually, all the members of both gangs assemble on either side of Tony's body, showing that the feud is over. The Jets and Sharks form a procession, and together they carry Tony away, with Maria the last in the procession.