28-year-old factory worker Will Salas (Justin Timberlake) lives with his 50-year old mother Rachel (Olivia Wilde) in the ghettos. One day, Will and his 29-year old best friend Borel (Johnny Galecki) save rich 105-year-old Henry Hamilton (Matt Bomer) from suffering a time-robbery assault in a bar where he flaunts his time around buying people drinks. Hamilton is attacked by Fortis (Alex Pettyfer), the 75-year old Briton mobster boss of a gang called the Minutemen. Will leads Hamilton to safety, where Hamilton says to Will, "For few to be immortal many must die", as there is essentially enough time for everyone to live a full life, but it is stockpiled for the rich to become immortal. An upset Will argues that no one should die before their time naturally ends so that others may live, upon which Hamilton describes how he no longer even desires life, in saying "though your body may not be worn out, your mind is. We want, we need, to die."
Later that night, Hamilton transfers all (116 years) but five minutes of his remaining time to the sleeping Will and starts climbing a bridge. As his time expires, he falls into the river below. Will arrives too late to save him, realizes he has been filmed by a nearby surveillance camera, and flees the area. Resident police force, the Timekeepers, have various theories as to his death. A young timekeeper, correctly assumes Hamilton had "timed out', a.k.a. killed himself, but 60-year old veteran Timekeeper Raymond Leon (Cillian Murphy) is convinced he was murdered by a Dayton resident. Will then visits Borel and gives him a decade's worth of time, as they have been friends for ten years.
Will awaits his mother at a bus station, only to discover that she didn't have enough time to pay for her usual bus ride after the price suddenly increased. He rushes down the street to find her. They encounter each other on foot, and as she runs and leaps into his arms, her time expires before her son can help her and she dies in his arms. Remembering what Hamilton told him about the inequity of the time system, Will decides to seek revenge, and leaves for New Greenwich, the wealthy time zone, with over a century on his clock. Upon arrival, he enters a casino, where he meets a 90-year old millionaire, time-loaning businessman Philippe Weis (Vincent Kartheiser) and his 27-year-old daughter Sylvia Weis (Amanda Seyfried). Sylvia becomes interested in Will after a tense gambling table showdown where Will beats her father in poker with only seconds to spare on his clock, and she invites Will to a party at her father's mansion.
At the mansion, Will is apprehended by Leon, who confiscates most of his time, but Will then escapes taking Sylvia hostage. Returning to the ghetto with her, he drives into an ambush of Fortis', who, in disappointment to find that the unconscious Will was in possession of Hamilton's time but lost it, steals most of Sylvia's, only failing to take the last half hour as the approach of the Timekeepers forces him to leave the scene. Will returns to consciousness and gives Sylvia some of his remaining time so they can return to his old neighborhood. They first visit Borel to retrieve some time Will gave him earlier as their time is running out soon, only to find out from Borel's grief-stricken wife that he has drunk himself to death with 9 years on his clock. Sylvia pawns her jewelry for a meager price of 2 days. Finding themselves shelter later, Will makes a call to Weis demanding a 1,000 years' ransom for Sylvia, to be distributed to the people of the ghetto. Leon traces Will's location from his phone call, and heads to Dayton in pursuit.
The following day, as Will prepares to release Sylvia, he discovers that Weis did not pay the ransom, but Will decides to let Sylvia go regardless. Leon appears and almost kills Will, but is shot in the shoulder by Sylvia. Will then transfers four hours of time to the disarmed Leon so that he is able to walk out of Dayton before he "clocks out". Will and Sylvia escape in Leon's car. Later, Will tells her that she still has a chance to walk away from the situation, but she decides to remain by his side, saying there is no purpose to the life she once had in New Greenwich. They begin a series of Time Bank robberies, stealing the Time Capsules which store time equivalents and distributing them to the poor, with a bounty of 10 years on their heads. Fortis eventually tracks down Will and Sylvia a second time, and challenges Will to a Time Fight. Will dominates the fight by using the technique he learned from his late father, then shoots the remaining Minutemen while Fortis dies in the time fight, his time transferred to Will.
Will and Sylvia realize their previous efforts were futile, as the rich have the power to simply increase the cost of living in the ghettos to maintain the status quo. They succeed in stealing a million years (1000000:00:0:00:00)from Weis' private headquarters in a Time Capsule, escaping all resistance on their way out and reaching Dayton. Upon arrival, Leon crashes his car into Will's, but Will is able to hand the Time Capsule to a young girl who then distributes the time among the people. Leon eventually catches up with Will and Sylvia outside the city, holding them at gunpoint. Will jokingly asks Leon to return some of the time he previously loaned him so that they can survive till their executions, but Leon realizes that he had neglected to replenish his own time before going after them (only 5 seconds left), and dies. Will and Sylvia are left with seconds to live, but Will runs to Leon's car and takes his allotted time, and transfers it to Sylvia seconds before she is about to die, a scene mirroring his mother's death. When Will completed transfering his time to Sylvia, He has 1 days remaining time.
Will and Sylvia continue robbing banks as part of their efforts to crash the system, now with a bounty of 100 years on their heads, while the rich attempt to cope with the sudden surge of people who now have enough time to change zones arriving from the ghettos. A news broadcast shows as the factories, in which also Will once worked, are no longer in action.