In Byzantine times, the town was also referred to as Λευκωσία (Lefkosia) or as Καλληνίκησις (Kallenikesis).

 In the 4th century AD, the town became the seat of bishopric, with bishop Saint Tryphillius (Trifillios), a student of Saint Spyridon.

After the destruction of Salamis, the existing capital of Cyprus, by Arab raids in 647, Nicosia became the capital of the island around 965, when Cyprus rejoined the Byzantine Empire. The Byzantines moved the island's administration seat to Nicosia primarily for security reasons as coastal towns were often suffering from raids. From that point on it has remained as the capital of Cyprus. Nicosia acquired a castle and was the seat of the Byzantine governor of Cyprus; the last Byzantine governor was Isaac Komnenos, who declared himself emperor of the island and ruled the island from 1183 to 1191.