Triptolemos was born in Eleusis, a small town on the western coast of Attica, the region around Athens, a place whose name would one day become synonymous with the most sacred religious rites in the Greek world. His father was Celeus, the king of Eleusis, and his mother was Metanira, the queen, though some traditions gave him different parents. The Homeric Hymn to Demeter, one of the oldest and most beautiful poems in Greek literature, calls him one of the sons of Celeus, a youth of the royal house who happened to be present when the goddess came to their door. Other sources, including some later poets and mythographers, claimed that he was the son of Oceanus and Gaia, a divine child who had always been destined to serve the goddess of the harvest. Either way, his life was changed forever by the arrival of a stranger.

The stranger was Demeter, the great goddess of grain and fertility, who had left Olympus in grief after her daughter Persephone was abducted by Hades, the god of the underworld. Hades had opened the earth and seized the girl while she gathered flowers in a meadow, and Demeter had wandered the earth for nine days and nine nights, refusing to eat or drink, her grief so terrible that the crops withered and the earth grew barren. On the tenth day she came to Eleusis, disguised as an old woman, weary and sorrowful. The daughters of Celeus found her by the well called Parthenion and brought her to the palace, where Metanira welcomed her as a guest. Demeter sat in silence for days, refusing wine and food, until Iambe, a servant woman of the household, made her laugh with bawdy jokes and dances. Then Demeter accepted a drink of barley and water, the kykeon, and her mood began to lift. But she did not reveal her identity. She asked to nurse the infant Demophon, the youngest son of Celeus and Metanira, and the queen, grateful for the old woman's kindness, agreed.

What happened next became one of the most famous episodes in Greek myth. Demeter anointed the infant Demophon with ambrosia, the food of the gods, and placed him in the fire each night to burn away his mortal nature and make him immortal. But Metanira, peeping into the room one night, saw her baby in the flames and screamed in terror. Demeter, enraged by the interruption, revealed herself in her true form, a goddess of terrible beauty and power, and told Metanira that she had destroyed the child's chance at immortality. Then she demanded that a great temple be built in her honour at Eleusis, and that the rites of the Mysteries be established there. It was at this point, according to the Homeric Hymn, that she turned her attention to Triptolemos, the youth of the royal house who had shown her kindness and who was ready to receive her greatest gift.

Demeter taught Triptolemos the art of agriculture. She showed him how to break the earth with the plough, how to sow the seed in straight furrows, how to tend the growing grain through the seasons, and how to harvest it with the sickle and thresh it on the stone floor. She gave him a great sack of grain, the first seed corn, and then she did something extraordinary. She gave him a chariot drawn by winged serpents, creatures of the earth that could fly through the air, and she commanded him to travel the world and teach every people the art she had taught him. The chariot rose into the air, and Triptolemos, a mortal youth who had never left the fields of Eleusis, found himself flying over mountains and seas, carrying the gift of grain to lands that had never known it.

His journeys took him across the known world and beyond. He flew to Greece first, landing in the fields of the Peloponnese and teaching the Argives, the Arcadians, and the Achaeans how to plough and sow. Then he crossed the sea to Crete, to Cyprus, to the islands of the Aegean, scattering seed as he went. He flew north to Thrace and south to Egypt, east to Phoenicia and west to Italy, and everywhere he landed he taught the people to break the soil and plant the grain. In some traditions, he also taught them the secret rites of the Mysteries, the initiations that Demeter had established at Eleusis, promising those who underwent them a blessed existence in the afterlife rather than the dim and joyless existence of ordinary ghosts. The spread of grain cultivation and the spread of the Mysteries went hand in hand, and Triptolemos was the agent of both.

But not every journey was peaceful. When Triptolemos flew to Scythia, the land of the northern barbarians, he was received by King Lynkos, a ruler who saw in the young man's gift not a blessing but an opportunity. Lynkos invited Triptolemos to a banquet and, while his guest slept, tried to kill him with a sword, intending to steal the serpent chariot and claim the discovery of agriculture for himself. But Demeter, watching over her messenger from Olympus, intervened. She struck Lynkos with a sleep so deep that he could not move, and when he woke he had been transformed into a lynx, the wild cat whose name he bore, a punishment for the man who had tried to murder the bringer of grain. Triptolemos escaped unharmed and continued his mission, but the story became a warning: the gift of agriculture was sacred, and those who tried to steal it would be punished by the goddess herself.

In other traditions, Triptolemos's travels were less violent but no less significant. He was said to have founded the city of Pisa in the Peloponnese, to have established the first harvest festivals in Thessaly, and to have taught the Etruscans of Italy the arts of the field. The Athenians claimed him as their own, for Eleusis was in Attica and the Mysteries were under Athenian control, and they portrayed him on their coins and in their public art as a symbol of Athens's civilising mission. The winged serpent chariot became his standard attribute in sculpture and vase painting, and he was often shown as a bearded man holding a sheaf of wheat, the very image of the farmer as hero.

When his work was done, Triptolemos returned to Eleusis and lived out his days as a priest of the Mysteries. Some said that Demeter made him immortal, granting him a place among the heroes who had served the gods faithfully. Others said that he died like any mortal and was buried in a tomb at Eleusis that was shown to visitors for centuries. In either case, his legacy was secure. The Eleusinian Mysteries, which he had helped to establish, became the most important religious institution in the Greek world, drawing initiates from across the Mediterranean for nearly two thousand years. The rites were secret, and those who underwent them were forbidden to speak of what they had seen, but the promise was clear: those who were initiated into the Mysteries would find happiness in the afterlife, freed from the fear of death that haunted ordinary mortals. Triptolemos, the first farmer, had become the first initiate, and through him the goddess's gift passed to all who came after.