Cersobleptes is the son of Cotys, king of Thrace, on whose death in 358 BCE he inherits the kingdom in conjunction with Berisades and Amadocus II, who are probably his brothers.

He is very young at the time, and the whole management of his affairs is assumed by the Euboean adventurer, Charidemus, who is connected by marriage with the royal family.

The area controlled by Cersobleptes is east of the river Hebrus.