27 years after the events of Terminator 2: Judgment Day, a new, modified liquid metal Terminator (Gabriel Luna) is sent from the future by Skynet in order to terminate Dani Ramos (Natalia Reyes), a hybrid cyborg human (Mackenzie Davis), and her friends. Sarah Connor (Linda Hamilton) comes to their aid, as well as the original Terminator, for a fight for the future.
- Linda Hamilton as Sarah Connor: The mother of John Connor, who will become the future leader of the Human Resistance in the war against the machines (Skynet). She hunts and kills Terminators to prevent Judgment Day and forestall the coming conflict.
- Arnold Schwarzenegger as T-800 "Model 101" / Carl: An aging Terminator, one of several sent back in time to kill John Connor in the past. Having abandoned its mission and living in seclusion, it is recruited by John's mother Sarah to help protect Dani Ramos.
- Brett Azar serves as the body double for the young T-800, while CGI will be applied to recreate Schwarzenegger's facial likeness from the 1990s in flashback scenes.
- Mackenzie Davis as Grace, a soldier-assassin converted into a cyborg and sent from the future to protect Dani Ramos from the new advanced Terminator prototype.
- Natalia Reyes as Daniella "Dani" Ramos, a young woman targeted for termination by the new advanced Terminator prototype.
- Gabriel Luna as Rev-9, an advanced Terminator sent back in time to terminate Dani, consisting of a traditional solid endoskeleton surrounded by a "skin" of mimetic poly-alloy. In contrast to the similar T-X, Rev-9 possesses the ability to separate these two components into two separate, fully autonomous Terminator units.
- Diego Boneta as Miguel, Dani's brother.
- Edward Furlong as John Connor: The son of Sarah Connor, portrayed as a messianic figure who was destined to save the remnants of mankind upon Judgment Day (a nuclear holocaust that would claim three billion human lives), years in the future, from an apocalyptic war against the machines (Skynet) as leader of the Human Resistance, as well as the more specialized resistance unit he personally led, Tech-Com.
- Jude Collie serves as the body double for young John Connor, while CGI will be applied to recreate Furlong's facial likeness from the 1990s in flashback scenes.