At first he shared his sovereignty with his father's friend John VI Cantacuzenus, and after a quarrel with the latter was practically superseded by him for a number of years (1347-1355).
His reign was marked by the gradual dissolution of the imperial power through the rebellion of his son Andronicus IV and by the encroachments of the Ottomans, to whom in 1381 John acknowledged himself tributary, after a vain attempt to secure the help of the popes by submitting to the supremacy of the Roman Church.
