Byzantine emperor, was the son of John VI. Cantacuzenus (q.v.). In return for the support he gave to his father during his struggle with John V. he was allowed to annex part of Thrace under his own dominion and in 1353 was proclaimed joint emperor. From his Thracian principality he levied several wars against the Servians. An attack which he prepared in 1350 was frustrated by the defection of his Turkish auxiliaries. In 1357 he was captured by his enemies, who delivered him to the rival emperor, John V.
Compelled to abdicate, he withdrew to a monastery, where he busied himself with writing commentaries on the Scriptures.