Due to the events shown in Terminator 2: Judgment Day, Judgment Day did not occur as originally predicted. Still not believing that it was completely prevented, John Connor is living "off the grid" in Los Angeles, California with no permanent residence, credit cards, or mobile phone and is working freelance so he can't be tracked. Skynet sends another Terminator, the T-X, back to July 24 2004, Judgment Day, to kill the human resistance's future lieutenants, because Connor could not be located through any information databases. The T-X, later dubbed the "Terminatrix", is armed with a full arsenal of advanced weapons from the future, avoiding the restriction of non-living tissue by carrying them internally, including the ability to remotely control most machines. The T-X, like the T-1000, has the ability to shift appearance, however, unlike the T-1000 the T-X merely has a sheath of mimetic polyalloy over its endoskeleton. The T-X has also been designed and programmed to destroy other cybernetic organisms, thus countering the threat of Terminators being reprogrammed by the Resistance.
As before, a reprogrammed Terminator, identical to the Terminators from the previous films, has been sent back in time to protect Connor and his future wife, Katherine 'Kate' Brewster. In a plot twist, this specific Terminator killed John Connor in 2032, before being reprogrammed and sent back in time by Connor's wife. After rescuing them from an initial attack, the Terminator leads them to the grave of Sarah Connor (who died of leukemia 7 years previous) in Victorville. However, they find the coffin filled with weapons (Sarah having been cremated in Mexico) which her friends placed in accordance with Sarah's will as a back-up for John to use in the event that Judgment Day was not prevented. The T-X and the police arrive, and the three narrowly escape in a hearse.
After the destruction of Cyberdyne Systems in T2, the US Air Force has taken over the Skynet project as part of its Cyber Research Systems division, headed by General Robert Brewster, Kate's father. In an attempt to stop the spread of a computer supervirus, they activate Skynet, allowing it to invade all of their systems: too late, they discover the virus is Skynet, which has been exerting its control over the global computer network under the guise of the virus. John, Kate, and the Terminator arrive just a few minutes too late to stop them. The T-X programs the T-1 terminators to kill office personnel and protect Skynet, which has become self-aware. Just before General Brewster dies, he tells them that the Skynet system core is in Crystal Peak, a base built into a mountain a short distance away by plane.
As they board a plane to leave, they are attacked by the Terminator, earlier injected with viral nanomachines by the T-X to control it. To avoid killing Connor, he shuts himself down. When they reach Crystal Peak, they are attacked once again by the T-X. Suddenly, a helicopter comes crashing through the front wall and into the T-X. The Terminator has managed to reboot himself and regain control. The T-X detaches its legs after they are crushed beneath the helicopter, quickly crawling after John and Kate. The Terminator manages to catch hold of the T-X, buying John and Kate enough time to get to safety: the Terminator remarks to John that "We will meet again!". With the pair safe, the Terminator shoves its last remaining hydrogen fuel cell in the T-X's mouth with a snide remark of "You are terminated!", destroying both of them in the resulting explosion.
John and Kate discover that the base does not house the Skynet core; it is an old fallout shelter for VIPs that predates John's birth. General Brewster sent them there to protect them from the nuclear holocaust to come. There is no Skynet core; Skynet is software running on thousands of computers throughout the world making Judgment Day unavoidable. Skynet begins a series of nuclear attacks across the world, commencing Judgment Day and starting the war of man versus machine. Foreshadowing Connor's future leadership role, when the confused military forces and ham radio operators ask for orders, he picks up the radio and takes command, giving orders to the confused survivors.
- T-850, played by Arnold Schwarzenegger
- John Connor, played by Nick Stahl
- Kate Brewster, played by Claire Danes
- T-X, played by Kristanna Loken
- Robert Brewster, played by David Andrews
- Scott Mason, played by Mark Famiglietti
- Dr. Silberman, played by Earl Boen
- Betsy, played by Moira Harris
- Chief Engineer, played by Chopper Bernet
- Brewster's Aide, played by Chris Lawford
- Rich woman, played by Carolyn Hennesy
- Westside Street Cop, played by Jay Acovone
- Roadhouse Bouncer, played by M.C. Gainey
- Roadhouse Clubgoer, played by Susan Merson
- Roadhouse Clubgoer, played by Elizabeth Morehead
- William Candy, played by Arnold Schwarzenegger (deleted scene)
- Non-Humanoid Hunter Killer
- Combat chassis
- Hydrogen fuel cell
- Head-up display
- Living tissue
- Mimetic Polyalloy
James Cameron announced T3 many times during the 1990s, but without coming out with any finished script. During his divorce with Linda Hamilton, she asked for the Terminator franchise rights which she promptly sold to Carolco Pictures owners Mario Kassar and Andrew G. Vajna. Tedi Serafian wrote a script, but as it would cost over $300 million, it was rejected. Serafian earned a "story" credit after screenwriters John D. Brancato and Michael Ferris used some of his ideas, like Sarah Connor being dead, and the rival Terminator being female.
The studios had long wanted to make a sequel to Terminator 2: Judgment Day. However, they weren't sure that Arnold Schwarzenegger would appear in it. Schwarzenegger initially refused to star in Terminator 3 because James Cameron, who created the character and directed the first two films, would not be directing the third installment. Schwarzenegger tried to persuade Cameron to produce the third film. Cameron declined, however, and feeling that the Terminator character was as much Schwarzenegger's as it was his own, he advised Schwarzenegger to just do the third film, and ask for "nothing less than $30 million."
The movie's final production budget was $187.3 million, making it the most expensive independently-produced movie in history. Schwarzenegger had to spend $6 million of his own money to help fund the production of the movie. It was a scene that he himself wanted to put in the movie, as he explains in the audio commentary. Schwarzenegger agreed to defer part of his salary in order to prevent the relocation of the set to Vancouver, British Columbia from Los Angeles. Many pundits saw this as preparation to his campaign for California governor, in which he emphasized giving incentives to have movie productions stay in California, rather than film in less-expensive places elsewhere. In that vein, the film was markedly "cleaner" than previous Terminator films, featuring significantly less violence and swearing.
The film takes several ideas from the novel T2: Infiltrator by S. M. Stirling. The novel, published in 2001, features a female terminator, the I-950, a plot point later reused in Terminator Rewired. The idea of Judgment Day being postponed was also used in the book. It also inspires the Sgt. Candy scene with its own explanation of the Terminator's physical appearance, in the form of Austrian counter-terrorist Dieter von Rossbach.
After T3 was released, Cameron would go on record as saying he "never planned on doing a third film, because the story was finished with T2." This conflicts with comments he made during the making of the Universal Studios ride T2 3-D: Battle Across Time, in which he stated that it was a "stepping stone to a third theatrical production." This comment can be seen on "The Making of T2 3D" as an extra on the T2 Ultimate Edition DVD.
Filming began on April 12, 2002.
- According to the producers of the 2008 TV series Terminator: The Sarah Connor Chronicles, the events of T3 take place in an alternate timeline to the events of the TV series, and indeed there are numerous differences between the two productions, such as the fate of Sarah Connor, and the revelation in T3 that Judgment Day still takes place; the series has also (so far) omitted any reference to Kate Brewster.
- T3 also contradicts the extended version of Terminator 2, which included an epilogue (cut from the theatrical release but included in home video extras and TV versions) showing an elderly Sarah Connor in a world that never experienced the nuclear war that ends T3.
- John Connor states that he was 13 when the T-1000 tried to kill him, however according to T2 he was 10 when the T-1000 tried to kill him. It is likely he remembered incorrectly because, if he was 13, then Judgment Day would have happened before the events of T2.
- T-X shoots Elizabeth Anderson - after killing William Anderson, the T-X goes upstairs to kill Elizabeth. The scene was not entirely filmed as Mostow believed that it was redundant.
- T-X shoots the Wrong Kate - in the film, the T-X shoots a person she misidentifies as Kate offscreen. This scene shows the T-X shooting the woman instead of the audience (and Kate) simply hearing it.
- CRS Preview and Seargent Candy - One scene filmed for T3 but removed from the final release is a comedic sequence expanding on the film's revelation that Skynet and the terminators were invented by the US military. The scene shows that the T-800 and T-850 model terminators seen in the three films were based upon Sgt. William Candy, a burly and somewhat dim-witted Southerner; when an official questions the suitability of Candy's accent (dubbed by an uncredited actor), an aide, speaking with Schwarzenegger's overdubbed voice, states that the voice can be fixed. This deleted scene is included with the DVD release of the film.
- "I was made here" - An extended version of the scene in General Brewster's office, where Brewster identifies the T-850 as Seargent Candy. The T-850 replies, "Negative. I was made here." With the deletion of the Seargent Candy scene, this scene was also removed.
- Extended T-X vs T-850 - cut from the movie were additional scenes of the T-X and the T-850 fighting in CRS, including a scene where the T-X slams the T-850 into the ceiling of the corridor several times, the T-850 headbutting the T-X, and the T-X biting into the T-850's skin, morphing her jaws into a mechanical set of jaws.
- Alternative Ending - an alternative ending was partially shot where another T-850 would appear in Crystal Peak and destroy the Skynet system core. This ending was to be used in the event focus groups disagreed with the official ending.
- It is interesting to note that the film received a "12" rating in the UK, despite John using the word "fuck" and "fucking" and a scene showing the T-X taking control of a police car by sticking its arm through the driver. (Incidences of this are unusual, the BBFC normally rates any film with an "f" word in it and violence like that a "15").
- This is the first film where a HK-Tank is absent from the Future War sequences.
- The reason this new Skynet is nearly identical to the old one might be the fact that the T-800 from Terminator 2 left his left arm stuck in the gears, and they used THAT to create Skynet.