Aeson was born to King Cretheus of Iolcus and his wife Tyro, the daughter of King Salmoneus. Cretheus was a son of Aeolus, the keeper of the winds, and had founded the city of Iolcus on the coast of Thessaly. Aeson had two full brothers, Pheres and Amythaon. But Tyro had also been visited by Poseidon, the god of the sea, who disguised himself as the river god Enipeus to lie with her, and from that union were born twin sons, Pelias and Neleus. Tyro exposed the infants on a mountain, but a herdsman found them and raised them. When they grew to manhood, Pelias and Neleus returned to Iolcus, killed their stepmother Sidero for mistreating Tyro, and seized power. Pelias banished Neleus and the half-brothers Pheres and Amythaon, but he kept Aeson alive in the palace dungeons, a prisoner of the throne that was rightfully his.

While imprisoned, Aeson married a woman named Alcimede, though some call her Polymede or Amphinome. She bore him a son, and Aeson knew that Pelias would kill any heir who threatened his stolen crown. Alcimede therefore pretended that the baby had died at birth. She held a mock funeral and smuggled the living infant to Mount Pelion, where the centaur Chiron, the wisest of his kind and trainer of heroes, raised the boy in a cave. They named him Jason. Years later, Alcimede bore Aeson a second son named Promachus. The two boys grew up apart, one in a palace prison and one in a mountain cave, both hidden from the usurper's eye.

When Jason was twenty years old, he came down from Mount Pelion and travelled to Iolcus to claim his father's throne. He lost one sandal in the river Anaurus while helping an old woman across, not knowing she was Hera, the queen of the gods, who hated Pelias for murdering her priestess Sidero in her own temple. Pelias had been warned by an oracle to beware a man wearing one sandal. When Jason arrived at the palace with a single bare foot, Pelias recognised the prophecy but could not kill him in front of gathered kings. Instead he sent Jason on a quest to fetch the Golden Fleece, the golden hide of a flying ram that hung in Colchis under the guard of a never-sleeping dragon. Jason built the ship Argo, gathered fifty heroes called the Argonauts, and sailed into legend.

While Jason was away, Pelias told Aeson and Promachus that the Argo had sunk and all were dead. In despair, Aeson drank bull's blood, which kills a man as surely as any serpent's venom, and died. But in the more famous telling, Aeson survived into old age, weakened and grey, until Jason returned victorious with Medea, the sorceress-princess of Colchis and granddaughter of Helios the sun god. Jason begged Medea to save his father. Medea agreed, but warned that such magic was forbidden and dangerous. She spent nine nights in prayer and ritual, then flew across Thessaly in a chariot drawn by dragons, gathering herbs and strange substances from nine regions. She built two altars, one to Hecate, the goddess of witchcraft and crossroads, and one to Hebe, the goddess of youth. She slaughtered a black-fleeced sheep, poured its blood into trenches, and lit torches in the blood. She placed Aeson on a litter, put him into a magical sleep, and purged his body three times with fire, three times with water, and three times with sulphur.

Then Medea boiled her gathered herbs in a great bronze cauldron. She stirred the mixture with a withered olive branch, and as it circled through the liquid the branch turned green, sprouted leaves, and hung heavy with olives. Wherever the bubbling foam spilled upon the ground, flowers and soft grass sprang up. Seeing these signs that the potion was ready, Medea drew a blade and cut Aeson's throat, draining every drop of his old blood. She poured the rejuvenating brew into the wound and into his mouth. His white hair turned black, his wrinkles smoothed away, his leanness filled with new flesh, and his limbs grew strong. Aeson rose from the cauldron marvelling at himself, restored to the vigour of forty years before.

The same magic that saved Aeson destroyed Pelias. Medea demonstrated the rejuvenation technique to Pelias' daughters by cutting up an old ram and boiling it in the cauldron, producing a young lamb. She promised to do the same for their father, but this time she withheld the essential herbs. The daughters cut Pelias to pieces and threw him into the pot. He did not emerge. The usurper was dead, but Jason was now tainted by association with the crime, and Pelias' son Acastus drove Jason and Medea into exile. Aeson, whether restored to youth or already dead by his own hand, never sat upon the throne of Iolcus again. The kingdom passed to Acastus, and Aeson's legacy lived on only through his son's fame and the bronze cauldron that had turned an old man young.