Timarchus or Timarch is a usurper in the Seleucid empire between 163-160 BCE.

A Greek aristocrat, possibly from Miletus in Asia Minor, Timarchus is a friend of the Seleucid prince Antiochus IV Epiphanes during his time as hostage to Rome.

He is appointed satrap of Media in western Iran when Epiphanes becomes king in 175 BCE, and his brother Heracleides become minister of the royal finances.

The Persian part of the empire is threatened by the Parthians kingdom, and Timarchus probably spends much of his time reinforcing the defenses.

The Seleucid realms probably extend as far as the area of Teheran during this time.