In 88 BC as a part of the First Mithridatic War, Archelaus and his brother were involved in a military campaign with the Pontic army against King Nicomedes IV of Bithynia.
Archelaus was next involved in Mithridates VI’s successful military campaign in conquering most of the Roman Province of Asia.
After occupying Athens the Pontic army spent three days unsuccessfully fighting Quintus Bruttius Sura, a legate to the propraetor of Macedonia Gaius Sentius, with his small detachment of Roman soldiers.
Archelaus and Bruttius' forces battled thrice at Chaeronea before the Mithridatic host was defeated and repulsed, marking the first successful Roman engagement against the armies of Mithridates VI.
[10] The presence of the Pontic army under the command of Archelaus encouraged citizens from Southern Greece to revolt against Roman rule.
[9] Archelaus and his Athenian allies lost control of Piraeus and Athens; they were pushed back to the peninsula of Munichia.
[9] When Mithridates VI heard the news of the disastrous defeats, he ordered Archelaus to make peace with Sulla.
[9] The final terms of Sulla were that Mithridates VI should surrender part of the Pontic fleet and all conquered territory in Asia and pay an indemnity of 2,000 talents, in return for becoming a friend and ally of Rome.
Archelaus received from Sulla large estates in Greece, including 6,600 acres of land in Boeotia, and was referred to as a friend and ally of the Roman people.
Archelaus had married an unnamed Greek woman, possibly a Pontic princess, one of the daughters of Mithridates VI.