Nicomedes III Euergetes (Greek: Νικομήδης Εὐεργέτης Nikomḗdēs Euergétēs) was the king of Bithynia, from c. 127 BC to c. 94 BC. He was the son and successor of Nicomedes II of Bithynia by an unnamed woman.
The first wife of Nicomedes III, was the Cappadocian Princess Nysa, daughter of the Monarchs Ariarathes VI of Cappadocia and Laodice of Cappadocia. By Nysa, Nicomedes III had two sons who were Nicomedes IV of Bithynia, Socrates Chrestus and a daughter called Nysa. Nicomedes III and Nysa were distantly related as they held lineage from the Seleucid dynasty, the Antipatrid dynasty and the Antigonid dynasty.
He made himself for a time master of Paphlagonia. After the deaths of his first wife and father-in-law, in order to have a claim on Cappadocia, Nicomedes III married his former mother-in-law as his second wife. Laodice who had fled to him when King Mithridates VI of Pontus (Laodice’s first brother) endeavoured to annex the country. With Laodice's two sons Ariarathes VII and Ariarathes VIII dead, Nicomedes III brought forward an impostor as a claimant to the throne; but the plot was detected. The Roman Senate refused to recognize the claim, and required Nicomedes III to give up all pretensions to Cappadocia and to abandon Paphlagonia.
When Nicomedes III was asked to provide troops for Roman Statesman Gaius Marius´ war on the Cimbri and Teutones in transalpine Gaul in 104 BC he turned down the request declaring: "All those eligible for military service in my kingdom have been robbed by the Roman tax-farmers and sold into slavery".