Clearchus was given command of fifteen triremes with the goal of breaking through the blockade, and after being engaged by the Athenian navy, he was able to reach Byzantium after losing three ships.

After the final defeat of Athens, Clearchus returned to Sparta and appealed to the ephors, asking to be given a force to settle the political dissensions then rife at Byzantium and to protect the city and the neighboring Greek colonies from Thracian attacks.

He was granted that force, but when the ephors learned that the citizens of Byzantium considered him a tyrant, they recalled him through a messenger that reached Clearchus while he was still in the Isthmus of Corinth.

On Cyrus's death Clearchus assumed the overall command of the Ten Thousand and conducted the retreat of the army, aiming to fall back to the Tigris river while parleying with the Persians.

He was invited to a banquet by the satrap of Lydia and Ionia and general for Artaxerxes, Tissaphernes, but he and his party were arrested and sent to the royal court at Babylon, where he was executed on the orders of Queen Stateira.