Since 1060 Gregory served in Byzantine army. In 1064 he had achieved a significant position among the Byzantine military aristocracy, but failed at defending Ani against the Seljuk leader Alp Arslan, King Bagrat IV of Georgia and Albanian King Goridzhan in the same year. Since 1071 he was appointed as a "Strategos" (governor) of the theme of Iberia. As the Seljuk advance forced the Byzantines to evacuate the eastern Anatolian fortresses and the theme of Iberia, Gregory ceded control over Kars and Tao to King George II of Georgia in 1074. This did not help, however, to stem the Turkish advance and the area became a battleground of the Georgian-Seljuk wars.