Miller was introduced after Kate tells Faith to go to him in a Pre-Chapter cut scene. He is notably different to the other characters in Mirror's Edge because of his all white suit (matching his white hair) and a pair of high-caliber pistols (powerful, for it can kill heavily armored forces with a single round). At the beginning he doesn't trust Faith, because Kate never mentioned her Runner sister. But after a bit of persuasion he trusts Faith in her accusation that Kate did not kill Robert Pope (though he told Faith that he already knew Kate wouldn't do such a thing).
Like Faith, Miller went on a search for clues to prove Kate's innocence. He even arranged a meeting with Travis Burfield, while Faith was hiding nearby.
In the final chapter The Shard, Miller goes to the Shard (the building that controls the whole city's power and is a direct route to all police radios) and was partnered with a pair of Pirandello Kruger heavy armored guards. When Faith was ambushed by them, Miller kills the guards with his high-powered pistols. Helping the Runner by guiding her with the security cameras and communication (like Mercury), he was soon discovered and gunfire was heard in the security room he was in, abruptly cutting off communication. His current status is unknown.