Gorgo was born during the reign of her father Cleomenes I. She was his only child and is mentioned by Herodotus as having warned her father in 500 BC to send away Aristagoras of Miletus before he could corrupt him. Aristagoras was trying to get Sparta's involvement in the Ionian Revolt and resorted to bribery after Cleomenes' repeated refusals to become involved.
Cleomenes was jailed by the ephors and his half-brothers around 489 BC. Days later, he was found dead - possibly murdered - though officials claimed he committed suicide. Gorgo became his sole heiress and, at about this time married her father's half-brother and successor Leonidas who was probably in his late 40s and may have had a part in Cleomenes' death. The marriage may have been one of convenience to keep the property of the dead man within his family. Gorgo and Leonidas had one son - future King Pleistarchus.
Gorgo is credited with uncovering the message that Persia intended to invade Greece in 485 BC. Exiled former King Demaratus had sent two wooden tablets, covered with wax, through a messenger to Sparta. Gorgo suggested the wax be scrapped off and the message was revealed.
Five years later, her husband Leonidas led a contingent of 300 Spartans to Thermopylae to fight the Persian invaders. On his departure, Gorgo, certain of his death, asked him what should become of her. Leonidas told her to marry a good man and raise good children.
Gorgo is one of few ancient Greek women that is treated with respect and honour by the ancient writers for her strength of character, her cunning and bravery.