In 2154, Earth is overpopulated and polluted. Most of the earth’s citizens live in poverty, on the edge of starvation, and with little technology and medical care. The rich and powerful live on Elysium — a gigantic, terraformed space habitat located in Earth’s orbit. Elysium is technologically advanced with some of its technology including Med-Bays: medical machines that can cure all diseases, reverse the aging process and regenerate new body parts. A long-running feud exists between the wealthy residents of Elysium and the citizens of Earth, who want Elysian technology to cure their medical ailments.
Max Da Costa (Matt Damon), a former car thief on parole lives in the ruins of Los Angeles, and works at an assembly line for Armadyne Corp, a company run by John Carlyle (William Fichtner), who originally designed Elysium, and now supplies its weaponry as well as the robots that police Earth. During an industrial accident at the factory, Max is trapped in a chamber and is hit by a lethal dose of radiation. After being rescued he is informed that he has five days to live before succumbing to radiation poisoning. Desperate for a cure, he and his friend Julio (Diego Luna) seek help from a human smuggler named Spider (Wagner Moura) to get him to Elysium; his only chance for survival is using a Med-Bay.
Meanwhile, when a trio of ships full of illegal immigrants from Earth attempts to reach Elysium and its Med-Bays, Elysian Secretary of Defense Delacourt (Jodie Foster) orders a sleeper agent, Kruger (Sharlto Copley), to destroy the shuttles. While two of the shuttles are shot down in space, killing everyone on board, the third shuttle makes it but once on Elysium, everyone on board is either killed or arrested and deported. Elysian President Patel (Faran Tahir) reprimands her for her immoral and unsubtle methods, and threatens to fire her unless she tones down her actions. Regarded as a loose cannon, Kruger is dismissed from service. Delacourt, vowing to protect Elysium and her own power, bargains with John Carlyle to create a program that can override Elysium’s computer core to give her the Presidency. Carlyle stores the reboot program in his brain for transport to Elysium and encrypts it with a lethal protection program.
Spider agrees to get Max to Elysium if he can steal financial information from Carlyle. To assist him, Spider’s men surgically attach a powered exoskeleton to Max. With Julio and a team of Spider’s men, Max shoots down Carlyle’s ship, and in the ensuing firefight with Carlyle’s security droids, Carlyle is fatally wounded. Max downloads the program to his suit’s neural implant, but realizes that the encryption makes it unusable. Alerted to the data theft by Carlyle’s medical implant, Delacourt secretly reinstates Kruger and deploys him to recover the program. In the ensuing firefight, Julio is killed, and Max is wounded. He reaches out to his childhood friend Frey (Alice Braga), now a nurse, whose daughter Matilda has leukemia. Frey begs Max to take Matilda to Elysium to be cured, but Max refuses in order to protect them. Soon after Max leaves, Kruger, alongside his lackeys, Drake and Crowe, arrive, and after brutally interrogating Frey for information, they take her and Matilda prisoner aboard Kruger’s ship, while his drones hunt for Max. Delacourt orders an airspace lockdown over Los Angeles to buy enough time to recover Carlyle’s program.
Max delivers the program to Spider, who discovers that the program can be used to make all Earth residents Elysian citizens. However, because the lockdown makes it impossible to leave Earth, Max bargains with Kruger to be taken to Elysium, unaware that Kruger has already found out that Frey assisted Max and is holding her and Matilda hostage on the ship. As Kruger’s ship leaves Earth, Spider and his men take advantage of the lockdown lift and also board a ship towards Elysium. Meanwhile, in Kruger’s ship, a fight ensues and Kruger is grievously wounded by a grenade blast, which also disables the ship’s engines. After Kruger’s ship crashes on Elysium, Max, Frey and Matilda, who has been knocked unconscious during the crash landing, are arrested and taken to Delacourt, who orders the download of the program, despite the fact that it will kill Max. Delacourt also orders Frey and Matilda to be locked in an armory room.
After being restored in a Med-Bay by Drake and Crowe, a defiant Kruger kills Delacourt after she chastises him for his recklessness. After throwing Delacourt’s body in the room with Frey and Matilda, Kruger taunts Frey, stating his intentions to make sure Matilda will not be cured. On Kruger’s orders, Drake and Crowe exterminate the Elysian political officers in order to seize control for themselves; they also get orders from Kruger to murder Frey and Matilda. Meanwhile, having escaped his confinement, Max, knowing that Med-Bays only work for Elysian citizens, resolves to use Carlyle’s program to give everyone on Earth Elysian citizenship. Max arrives at the armory room and intercepts Crowe who is attempting to sexually assault Frey, kills him and Drake and frees Frey and Matilda. Max then meets up with Spider, who has one of his members escort Frey and Matilda to a nearby Med-Bay. They then head for Elysium’s core but are ambushed by Kruger, now equipped with a military-grade exoskeleton far superior to Max’s. In the ensuing fight, Max manages to rip out Kruger’s neural implant, rendering his suit immobile. However, Kruger tethers himself to Max’s suit and arms a grenade with the intent of killing them both. Max rips off the tether and hurls Kruger over a ledge to his death.
Spider and Max reach Elysium’s computer core, where Spider realizes that the program’s activation will kill Max. Max personally activates the program, having spoken a last time with Frey via radio. As Max dies, Elysium’s computer core reboots and registers every Earth resident as an Elysian citizen. President Patel arrives with security guards but the robots refuse to arrest Spider, whom they now recognize as a citizen. Matilda is cured by a Med-Bay and Elysium’s computer dispatches a huge fleet of medical ships to begin treatment of the citizens of Earth.