In c. 1304, he was sent to the court of the Serbian ruler Stephen Uroš II Milutin, intended to become his successor; his stay there was short, however, and he soon returned to Constantinople.
[1] In the Byzantine civil war of 1321–1328, between his father and his nephew, Andronikos III Palaiologos, Demetrios sided with the former.
In 1327–1328, during the last stage of the civil war, he served as governor of Thessalonica, although he may have been appointed to the post as early as 1322.
[1] Eventually he was forced to flee to Serbia, while Andronikos III managed to take his wife and children captive.
[1] Demetrios was accused of conspiring against his nephew in 1336/37, but Andronikos III dropped the charges.