In 2044, the United States has suffered economic collapse, causing severe social decay and growth in organized crime. In addition, a strange mutation has occurred in 10% of the population, giving them minor telekinetic powers, manifested by their ability to float small objects. They are referred to as TKs.
Thirty years into the future in 2074, time travel is invented, but is immediately outlawed. However, because by that point tracking technology has rendered it nearly impossible to dispose of bodies secretly, crime bosses turn to time travel to send their targets to the past to be killed using "loopers": hired guns paid in silver to kill whoever is sent to them.
The victims have bags over their heads, and silver bars strapped to their backs. When crime bosses want to end a looper's contract, they send his older version back to be killed by his younger self, referred to as "closing the loop".
Joseph "Joe" Simmons (Gordon-Levitt), 25, works for a mafia company in Kansas City as a looper. Joe's boss, Abe (Jeff Daniels), was sent back in time to manage the loopers and also owns a club where Joe frequents and spends time with Suzie (Perabo), a showgirl.
Abe also controls the "Gat Men", his muscle, led by Kid Blue (Segan). While at the club one evening, another looper announces that he has just closed his loop. After killing the victim, he finds gold instead of silver, and recognizes his older self. The big payoff is reason to party. Joe notices that loops are being closed at an increasing pace.
One night, Seth (Dano), Joe's friend and a fellow looper, visits him in a panic telling him that he was supposed to close his own loop but couldn't do it. Seth reports that his victim appeared, singing a song his mother had sung to him when he was a baby.
He couldn't kill him. Old Seth tells Seth that a person called the Rainmaker has taken over organized crime and is closing all loops for unknown reasons. The Gat Men then knock on Joe's door, so he hides Seth in his apartment floor safe.
The Gat Men suspect Joe is shielding Seth, so they take him in to Abe. Abe makes a deal with Joe. If he gives up Seth, he will walk free. If he doesn't, he can't be killed, as it will upset things in the future, but they can definitely make things difficult for him by taking the silver he has been hoarding for his retirement in France.
Joe immediately gives up Seth. Abe suggests Joe go to China instead of France. "Don't go to France. Go to China. I'm from the future. I know these things."
Old Seth attempts to climb a barb-wire fence, but notices old scars appearing on his arm, spelling out words telling him to go to an address. He ignores this, and one of his fingers disappears. Shortly after, another finger is gone.
The stubs are not bloody - as if the digits were removed many years earlier. Then the tip of his nose is cut off. Old Seth returns to his car, and heads for the address he was given.
Running toward it, he loses a foot, then apparently both feet, and he falls to the ground and crawls to the door. He bangs on the door, and it is opened by one of the Gat Men, who immediately shoots him.
Behind the shooter, we can see Young Seth, alive on a table where they were chopping off his body parts, and we hear the sound of a ventilator. Joe continues to do killings. After each killing, he visits a diner, and works on his French lessons.
He is served by a waitress named Beatrix. While waiting to do one killing, he is puzzled when the victim is late. When the person does appear, he has no bag over his head. Joe recognizes Old Joe (Willis) as his older self, and tries to shoot him.
Old Joe spins around, and uses the gold on his back to deflect the bullet. He grabs a gold bar and throws it at Joe, then knocks him out with a punch. Joe comes to, and finds a note, telling him to get out of town. Instead, Joe returns to his apartment, where he finds the Gat Men searching it and removing his silver.
He shoots one, but is winged by another, falls from his fire escape and blacks out. Flashback to Joe waiting for a victim. He kills him as usual, but sees that it is his older self, with the gold. This time, he has closed the loop. We step quickly through the next 30 years, and see Joe has a good retirement.
He moves to China, meets a beautiful, caring woman, and settles down. Then, after 30 years, he is grabbed, and prepared to be sent back to be killed. He manages to slip his wrist restraints, get his hood off, and kill his attackers. He then jumps into the time machine.