The dystopian nation of Panem consists of a wealthy Capitol ruling twelve poorer districts. As punishment for a past rebellion and as a way to demoralize the districts to quell social uprising, each district must provide two "tributes" - one boy and one girl between the ages of 12 and 18 selected by lottery (the "Reaping") - every year to compete in the televised Hunger Games; they must fight to the death in a vast arena, with the sole survivor rewarded with fame and wealth.
In District 12, Katniss Everdeen volunteers to be the female Tribute when her younger sister Primrose is initially drawn. She and the male Tribute Peeta Mellark, a boy her age from the same village, are escorted to the Capital by chaperone Effie Trinket and their mentor Haymitch Abernathy, a past District 12 victor and severe alcoholic. Haymitch impresses on them the importance of gaining sponsors as they can provide gifts of food and supplies during the Games. During part of a series of interviews, Peeta publicly expresses his love for Katniss, which she initially takes as trying to earn sponsors' favor, but later learns his love is earnest. While training, Katniss observes the Career Tributes Marvel, Glimmer, Cato and Clove, from Districts 1 and 2, who have been illegally training for the Games since a young age.
At the start of the games, Katniss ignores Haymitch's advice and tries to acquire supplies from the Cornucopia, the central point of the arena, and narrowly avoids being killed; nearly half the Tributes are killed in the initial melee. Katniss tries to stay as far away from the other competitors but the gamemaster Seneca Crane directs his agents to trigger events on the field to force her back towards the others. She runs into the Careers, with whom Peeta has allied, and escapes up a tree, where she finds Rue, District 11's female Tribute, hiding. The two work together to knock a nest of poisonous tracker jackers onto the Careers, killing Glimmer and forcing the others to flee. Rue helps Katniss tend to her wounds, becoming friends, and they work a plan to secretly destroy a cache of supplies the Careers have been hoarding, causing the Careers to distrust each other. Marvel discovers them and kills Rue before Katniss can help her. Katniss shoots and kills Marvel with an arrow, then mourns for Rue's loss, making sure her moment of sorrow is captured on the broadcast. The people of District 11, taken by Katniss' action, start a riot. President Snow warns Crane that this turn of events does not bode well for the Games.
When Crane returns, Haymitch suggests that he alter the game rules to allow two winners to make things interesting. When this change is announced, with the stipulation that the winners have to be from the same district, Katniss searches for Peeta, finding him wounded after fleeing from the Careers. After moving him to safety, Katniss leaves to get medicine from the Cornucopia, where Clove attempts to kill her. Katniss is saved when Thresh, District 11's other tribute, arrives and kills Clove, believing she had killed Rue, sparing Katniss's life out of respect for the kindness she showed Rue. Katniss returns with the medicine and prepares Peeta for the final hours of the game. Crane sends out wild beasts that kill Thresh, leaving only Cato, Katniss, and Peeta alive. Katniss and Peeta make it to Cornucopia where Cato is waiting and threatens to kill them both as the wild animals approach. Katniss gets the upper hand, and Cato falls to the ground and is eaten by the beasts.
Morning arrives, and Katniss and Peeta are still alive. They think they are the victors, but Crane shuts the district rule down, only allowing one victor. Katniss then convinces Peeta to enact a double suicide with her by ingesting nightlock, which she had obtained in the woods. When the two are about to take the poison, Crane changes his mind again, because he sees that their double suicide will ruin the Games by eliminating anyone from becoming Victor. They are both crowned victors of the 74th Hunger Games. Haymitch warns Katniss she has made great enemies with her act of defiance. Snow condemns Crane to his death for being manipulated by Katniss and Peeta. In the end of the film, Snow is shown walking up a stairway, perhaps pondering his next course of action.