He was a former suitor of Helen of Troy and led a group of forty ships for the Aetolians, one of the larger contingents. The Iliad states that he received his lordship because the previous dynasty of Oineus and Meleagros had perished, so the power to rule was bestowed on him. He was one of the nine volunteers to fight Hector in one-to-one combat, but lost in the drawing of lots to Telamonian Aias.
In the Iliad, Poseidon impersonates Thoas to rally Idomeneus so that he will prevent Hector, who had just killed the sea god's grandson, and his forces from routing the Argives. Later, when Hector has broken through to the ships and the Trojan advance is pressing hard upon them, Thoas advises the Greeks' best warriors to take a stand against Hector and the advancing Trojans in order to allow the rest of the Greek army to retreat to safety. In the Aeneid, Aeneas names Thoas as one of those Greeks hidden within the Trojan Horse.