Sosibius (lived 3rd century BCE) is the chief minister of Ptolemy Philopator (221–203 BCE), king of Egypt.

Nothing is known of his origin or parentage, though he may have been a son of Sosibius of Tarentum; nor have we any account of the means by which he rose to power; but we find him immediately after the accession of Ptolemy (221 BCE), exercising the greatest influence over the young king, and virtually holding the chief direction of affairs.

He soon proves himself, as he is termed by Polybius, a ready and dexterous instrument of autocracy: it is by his ministration, if not at his instigation, that Ptolemy puts to death in succession his uncle Lysimachus, his brother Magas, and his mother Berenice.

Not long after, Cleomenes, of whose influence with the mercenary troops Sosibius had at this time dexterously availed himself, shares the same fate.