In 923, Kourkouas was appointed commander-in-chief of the Byzantine armies along the eastern frontier, facing the Abbasid Caliphate and the semi-autonomous Muslim border emirates. He kept this post for more than twenty years, overseeing decisive Byzantine military successes that altered the strategic balance in the region.

During the 9th century, Byzantium had gradually recovered its strength and internal stability while the Caliphate had become increasingly impotent and fractured. Under Kourkouas's leadership, the Byzantine armies advanced deep into Muslim territory for the first time in almost 200 years, expanding the imperial border. The emirates of Melitene and Qaliqala were conquered, extending Byzantine control to the upper Euphrates and over western Armenia. The remaining Iberian and Armenian princes became Byzantine vassals. Kourkouas also played a role in the defeat of a major Rus' raid in 941 and recovered the Mandylion of Edessa, an important and holy relic believed to depict the face of Jesus Christ.