Christian Bale as John Connor: The battle-experienced leader of the Tech-Com human resistance, who is now in his early thirties, is waging war against Skynet after it has destroyed much of humanity in a nuclear holocaust. Bale was the first person to be cast and signed on for the role in November 2007. McG talked extensively with Bale in England about the role, and they both agreed to move forward.Bale is a fan of the films, and liked the script. He has signed on to appear in two sequels.

He and McG kept working on the story every day. Anton Yelchin as Kyle Reese: A teenaged soldier and admirer of John Connor. In The Terminator, to ensure the survival of the human race, he was sent back in time, and fathered John with Sarah Connor.

Sam Worthington as Marcus Wright: A decommissioned Terminator, who befriends Connor and Reese. His last memory is of being on death row, and Connor is unsure of whether he is from the past or the future.

Terminator creator James Cameron personally recommended Worthington (whom he directed in Avatar) to McG.[10] Worthington tore a muscle on his left ribs during the first weeks of filming, but nevertheless insisted on performing his own stunts.

Bryce Dallas Howard as Kate Connor: John's wife, who is helping him build his resistance. Charlotte Gainsbourg was originally set to play the part, but left because of scheduling conflicts with another film.Moon Bloodgood as Blair Williams: A "a no-nonsense and battle-hardened" pilot in the resistance suffering from survivor guilt.Common as Barnes: A freedom fighter and John's right-hand man.Roland Kickinger as the prototype T-800. This will be the first Terminator film in which Arnold Schwarzenegger does not play the Series 800 Model 101 model, because he is serving his second term as Governor of California.

Nevertheless, he granted the Halcyon Company permission to use his likeness in the film. The Austrian-born Kickinger previously played Schwarzenegger in a 2005 biographical film on the A&E Network.Additional cast members include Jadagrace as Star,Chris Ashworth as Richter, Chris Browning as Morrison,and Jane Alexander.

Helena Bonham Carter has been confirmed to star in a "small but pivotal" role as a character named Serena, who may be the lead villain.