Mopsus, son of Ampyx and a nymph (sometimes named as Khloris), born at Titaressa in Thessaly, was also a seer and augur. In Thessaly the place named Mopsion recalled his own. The earliest evidence of him is inscribed on the strap of a soldier's shield, found at Olympia and dated 600-575 B.C. According to Diodorus Siculus (III.55), Mopsus was a Thrakian commander who had lived long before the Trojan War, and along with Sipylus the Skythian, had been driven into exile from Thrace by its king Lykurgus of Thrake. Sometime later, he and Sipylus defeated the Libyan Amazons in a pitched battle, in which their queen Myrine was slain, and the Thrakians pursued the surviving Amazons all the way to Libya.
Mopsus was one of two seers among the Argonauts (the other being Idmon) his method of divining the future was based on the fact that it was said he could understand the Augury language of birds, having learned augury from Apollo. He had competed at the funeral-games for Jason's father and was among the Lapiths who fought the Kentaurs. While fleeing across the Libyan desert from angry sisters of the slain, Mopsus died from the bite of a viper that had grown from a drop of Medusa's blood. Medea was unable to save him, even by magical means. The Argonauts buried him with a monument by the sea, and a temple was later erected on the site.
Ovid places him also at the hunt of the Kalydonian Boar, although the hunt occurred after the Argonauts' return and Mopsus' supposed death.