Very little is known about the Psycho Gundam Mk-III. It is unclear if like its predecessors has its cockpit located in the head or if it has a transformation mechanism, however is able to fly in the atmosphere through a Minovsky Craft System and probably has a Psycommu system. Its armament include multiple mega particle guns on the shoulders, legs and chest, and large beam sabers on both arms.
The Psycho Gundam Mk-III was secretly developed by the Nomad Council Military and piloted by Maria Nichols, a test subject for the extrasensory virus, who stolen the mobile weapon during a test.
Gloria Chanvalley encounters the Psycho Gundam Mk-III, piloted by Maria Nichols to block her way to Pixie. Despite its overwhelming firepower, Gloria managed to beat it single-handedly while killing her in battle.