Onias III is a Jewish High Priest, the son of Simon II.

He is described as a pious man who, unlike the Hellenizers, fought for Judaism.

Seleucus Philopator defrays all the expenses connected with the sanctuary and is friendly to the Jews.

According to 2 Maccabees, a traitorous official of the Temple, however, Simon the Benjamite, induces the king, through his official Heliodorus, to undertake the plunder of the Temple treasury; the attempt is not successful, and the Syrian court never forgives the high priest for its miscarriage.

When Antiochus IV Epiphanes becomes king, Onias is obliged to yield to his own brother Jason.

According to Josephus, Jason became high priest after the death of Onias, the latter's son, who bore the same name, being then a minor.

It is strange that both father and son should have been named Onias, and still more strange is the statement of Josephus that the high priest who succeeded Jason and was the brother of Onias and Jason, likewise was called Onias, and did not assume the name of Menelaus until later; for according to this statement there must have been two brothers of the same name.