At an unknown point during his life, Kallous trained in the arts of Sith sorcery and eventually was granted the title of Darth.
Once a Kaggath began between Darth Thanaton and the rising Sith Lord Kallig, Darth Kallous had been residing on Corellia for some time. Kallig had thwarted each of his opponent's attempts on his life, and Thanaton summoned an audience of Imperial dignitaries and Sith to one of Corellia's many government plazas. Darth Kallous was one of the many present, and was called upon to kill Kallig. Despite his considerable power, Kallous was defeated in a brief duel.