John V Palaiologos or Palaeologus (Greek: Ίωάννης Ε' Παλαιολόγος) was a Byzantine emperor, who succeeded his father in 1341 at age eight.
John V was the son of Emperor Andronikos III and his wife Anna, the daughter of Count Amadeus V of Savoy by his second wife Maria of Brabant. His long reign was marked by the gradual dissolution of imperial power amid numerous civil wars and the continuing ascendancy of the Ottoman Turks.
John V came to the throne at age eight. His reign began with an immediate civil war between his designated regent, his father's friend John Kantakouzenos, and a self-proclaimed council of regency composed of his mother Anna, the patriarch John XIV Kalekas, and the megas doux Alexios Apokaukos.
John VI Kantakouzenos was crowned co-emperor on 31 March 1347. Matthew Kantakouzenos was crowned co-emperor on 10 December 1354.