For some Chaos Space Marines, simply dedicating their souls to the gods is not enough. Pledging themselves fully to the service of Chaos, they allow daemons to possess their bodies, becoming willing hosts to these immaterial creatures. Such possession is usually agonising, as the daemons writhe within their new physical form, changing it to better suit their needs.

Possessed Chaos Space Marines are easily distinguished by their grotesque features and mutated bodies; they might have vicious claws, outlandishly warped muscles, waving tentacles, disfigured faces, whipping tails, spines, antlers and all manner of other physical abnormalities. Many have vicious talons, razor-sharp horns or huge fangs that they can use to rip through enemy armour and even gouge through the side of a tank. The daemon within a Possessed gives him great speed, strength and resilience, and it is for this reason that the Possessed are so willing to undergo such traumatic transformations. However, the life of a Possessed can be horribly short, as those unable to contain the daemonic essence within their bodies eventually mutate beyond all recognition and are consumed from within by the dark fire of Chaos.