In 1995, John Connor is ten years old and living in Los Angeles with foster parents. His mother Sarah Connor had been preparing him throughout his childhood for his future role as the leader of the Human Resistance against Skynet, but was arrested after attempting to bomb a computer factory and imprisoned at a mental hospital under the supervision of Dr. Silberman. Skynet sends a new Terminator, designated as T-1000, back in time to kill John. The T-1000 is an advanced prototype composed of a mimetic polyalloy that allows it to take on the shape and appearance of almost anything it touches, and transform parts of its anatomy into knives and other stabbing weapons. The T-1000 arrives under a freeway, kills a policeman and assumes his identity. Meanwhile, the future John Connor has sent back a reprogrammed T-800 (Model 101) Terminator to protect his younger self.
In 2029, Human Resistance leader John Connor (Jason Clarke) launches a massive final offensive against Skynet, an artificial general intelligence system seeking to eliminate the human race. Before the Resistance wins the offensive, Skynet activates a time machine and sends back a T-800 Terminator to 1984 to kill John's mother, Sarah Connor (Emilia Clarke). John's right-hand man, Kyle Reese (Jai Courtney), volunteers to travel back in time to protect her. As Kyle floats in the machine's magnetic field, he witnesses John being attacked by another Resistance soldier (Matt Smith). He then has visions from his childhood about events in 2017.
John Connor has been living off the grid in Los Angeles in the years following the death of his mother, Sarah, from leukemia. Although Judgment Day did not occur on August 29, 1997, as expected, John still believes that a war between humans and the machines will occur. Unable to locate John in the past, Skynet sends a new model of the Terminator called the T-X back to July 24, 2004 to kill other members of the Human Resistance. The T-X is more advanced than previous Terminators, and has an endoskeleton with built-in weaponry, a liquid metal exterior similar to the T-1000, and the ability to reprogram other machines. Unlike previous Terminators, its standard appearance is female. The Resistance sends a reprogrammed Terminator (T-850 - Model 101) back in time to protect the T-X's targets including John and his future wife, Kate Brewster.
In 2003, Dr. Serena Kogan (Helena Bonham Carter) of Cyberdyne Systems convinces death row inmate Marcus Wright (Sam Worthington) to sign over his body for medical research following his execution. One year later, the automated Skynet system is activated, begins to perceive humans as a threat, and eradicates much of humanity with nuclear weapons in the event known as "Judgment Day".
In 2028, multinational conglomerate OmniCorp revolutionizes warfare with the introduction of robotic peacekeepers capable of maintaining law and order in hot spots such as Iran. Led by CEO Raymond Sellars, the company moves to market its tech to domestic law enforcement, but the passage of the Dreyfus Act, forbidding deployment of drones on U.S. soil, prevents this. Aware that most Americans oppose the use of military systems in their communities, Sellars asks Dr. Dennett Norton and his research team to create an alternative. The result is a proposal for a cyborg police officer. However, Norton informs Sellars that only someone who is stable enough to handle being a cyborg can be turned into one, and some candidates are rejected.
On May 12, 1984, two beings from the year 2029 arrive in Los Angeles: one is a Terminator T-800 Model 101, a cyborg assassin programmed to kill a young woman named Sarah Connor; the other is Kyle Reese, a soldier sent to protect her from the T-800. After the Terminator kills a gang member, a gun-shop manager, the two other women named "Sarah Connor" listed in the telephone directory, Sarah's roommate Ginger, and her partner, it tracks its target to the Technoir, a nightclub. Kyle arrives and saves Sarah from the Terminator. The two steal a car and escape, while the Terminator steals a police car and pursues them.
In a dystopian near-future, Detroit, which is now bankrupt and overrun with crime, gives Omni Consumer Products (OCP) control of its struggling police force. The company plans to replace the poor, run-down sections of Old Detroit with the high-end "Delta City," but must first address the city's high crime rate. As an alternative to existing law enforcement, OCP senior president Dick Jones (Ronny Cox) offers the prototype ED-209 enforcement droid, but it accidentally kills a board member during a demonstration. The OCP chairman, nicknamed "The Old Man" (Dan O'Herlihy), decides instead to back Jones' young rival, Bob Morton (Miguel Ferrer), and his experimental cyborg police officer program, "RoboCop.
In the year after the success of the RoboCop program and Jones's death, Omni Consumer Products (OCP) has created a new plan to have Detroit default on its debt so that OCP can foreclose on the entire city, take over its government, and replace the old neighborhoods with Delta City, a new planned city center independent of the United States government, enabling them to effectively have an entire city to be controlled by OCP.
After Robocop 2, Detroit is on the verge of bankruptcy after a series of failed business plans and drop of stocks, and are now struggling with their plans to create the new Delta City. To speed up the process, OCP creates an armed force called the Urban Rehabilitators, nick-named "Rehabs," under the command of Paul McDaggett (John Castle). Ostensibly its purpose is to combat rising crime in Old Detroit, augmenting the ranks of the Detroit Police Department in apprehending violent criminals. In reality, it has been set up to forcibly relocate the residents of Cadillac Heights. Nikko, a Japanese-American computer whiz kid, loses her parents in the process.
En 2030, la majorité du Midwest est ravagé et transformé en désert par le réchauffement climatique. Afin de contrôler la récession économique, une agence gouvernementale américaine appelée « Le Bureau de l'Humanité » traque les membres de la société considérés comme improductifs pour les isoler dans une colonie supposée paradisiaque nommée « Nouvel Eden ».