By most accounts, she was the daughter of Helios, the Titan sun god, and Perse, one of the three thousand Oceanid nymphs. Her brothers were Aeëtes, keeper of the Golden Fleece, and Perses. Her sister was Pasiphaë, the wife of King Minos and mother of the Minotaur. Other accounts make her the daughter of Hecate, the goddess of witchcraft. She was often confused with Calypso, due to her shifts in behavior and personality, and the association that both of them had with Odysseus.
In Homer's Odyssey, an 8th-century BCE sequel to his Trojan War epic Iliad, Circe is initially described as an enchantress living in an isolated palace that stands in the middle of a clearing in a dense wood on her (fictitious) island of Aeaea. Around her home prowls strangely docile lions and wolves fawned on all newcomers as she drugged them with her sorcery  Her gentle facade of lovely singing and working at an enormous loom. She invited the hero Odysseus' crew to a feast of familiar food, a pottage of cheese and meal, sweetened with honey and laced with wine, lures in Odysseus' crew. Upon entering her home, she provides a feast of familiar foods: a pottage of cheese and meal sweetened with honey and laced with wine, but also laced with one of her magical potions. She also had the crew drink out of an enchanted cup. With this trickery, Circe's magic turned them all into swine. Only Eurylochus, who suspected treachery behind the eerily peaceful and overly-welcoming palace facade and never went in, escaped to warn Odysseus and the others who had remained with the ship.
Before Odysseus reached Circe's palace, Hermes, the messenger god sent by Athena, intercepted him. Hermes acted as a mouthpiece for the gods as he delineated to Odysseus how exactly to execute his predetermined fate of defeating Circe to free his crew. Hermes provided Odysseus with the moly, that would protect him from Circe's magic. He also told Odysseus that once he resisted the magic, he must draw his sword and act as if he were going to attack her. From there, as Hermes foretold, Circe would ask Odysseus to bed, but Hermes advised caution, for the goddess would remain treacherous. Hermes describes how dangerous Circe could still take Odysseus' "manhood" unless he had her swear by the names of the gods that she would not do so. Odysseus followed Hermes' advice and was therefore able to free his men. They all then remain on the island for one year, feasting and drinking wine. According to Homer, Circe even advised Odysseus and his crew on how to return home, going so far as to suggest two alternative routes. She additionally gave directions to Odysseus so that he could visit the Underworld, something a mortal had never done. From the beginning to the end of this chapter of the Odyssey, Circe devolved from a powerful, independent goddess, therefore labeled an "enchantress", to a regular, mortal-like woman who served the needs of Odysseus and his crew, even cooking for and bathing them.
Towards the end of Hesiod's Theogony (c. 700 BCE), it is stated that Circe bore Odysseus three sons: Ardeas or Agrius (otherwise unknown); Latinus; and Telegonus, who ruled over the Tyrsenoi, that is the Etruscans. The Telegony, an epic now lost, relates the later history of the last of these. Circe eventually informed him who his absent father was and, when he set out to find Odysseus, gave him a poisoned spear. With this he killed his father unknowingly. Telegonus then brought back his father's corpse to Aeaea, together with Penelope and Odysseus' other son Telemachus. After burying Odysseus, Circe made the others immortal.
In the 5th-century CE epic Dionysiaca, author Nonnus mentions Phaunos, Circe's son by the sea god Poseidon.
According to Lycophron's 3rd-century BCE poem Alexandra, and John Tzetzes' scholia on it, Circe used magical herbs to bring Odysseus back to life after he had been killed by Telegonus. Odysseus then gave Telemachus to Circe's daughter Cassiphone in marriage. Some time later, Telemachus had a quarrel with his mother-in-law and killed her; Cassiphone then killed Telemachus to avenge her mother's death. On hearing of this, Odysseus died of grief.
In his 3rd-century BCE epic, the Argonautica, Apollonius Rhodius relates that Circe purified the Argonauts for the death of Absyrtus, possibly reflecting an early tradition. In this poem, the animals that surround her are not former lovers transformed but primeval 'beasts, not resembling the beasts of the wild, nor yet like men in body, but with a medley of limbs'.
Dionysius of Halicarnassus (1.72.5) cites Xenagoras, the 2nd-century BCE historian, as claiming that Odysseus and Circe had three sons: Rhomus, Anteias, and Ardeias, who respectively founded three cities called by their names: Rome, Antium, and Ardea.
Three ancient plays about Circe have been lost: the work of the tragedian Aeschylus and of the 4th-century BCE comic dramatists Ephippus of Athens and Anaxilas. The first told the story of Odysseus' encounter with Circe. Vase paintings from the period suggest that Odysseus' half-transformed animal-men formed the chorus in place of the usual Satyrs. Fragments of Anaxilas also mention the transformation and one of the characters complains of the impossibility of scratching his face now that he is a pig.
Some say she was exiled to the solitary island of Aeaea by her subjects and her father Helios for killing her husband, the prince of Colchis. Later traditions tell of her leaving or even destroying the island and moving to Italy, where she was identified with Cape Circeo.
The theme of turning men into a variety of animals was elaborated by later writers, especially in Latin. In Virgil's Aeneid, Aeneas skirts the Italian island where Circe now dwells, and hears the cries of her many male victims, who now number more than the pigs of earlier accounts:
The roars of lions that refuse the chain, / The grunts of bristled boars, and groans of bears, / And herds of howling wolves that stun the sailors' ears.
Ovid's 1st-century Metamorphoses collects more transformation stories in its 14th book. The fourth episode covers Circe's encounter with Ulysses (Roman names of Odysseus). The first episode in that book deals with the story of Glaucus and Scylla, in which the enamoured sea-god seeks a love potion to win Scylla's love, only to have the sorceress fall in love with him. When she is unsuccessful, she takes revenge on her rival by turning Scylla into a monster (lines 1–74). The story of the Latian king Picus is told in the fifth episode (and also alluded to in the Aeneid). Circe fell in love with him too; when he preferred to remain faithful to his wife Canens, she turned him into a woodpecker (lines 308–440).
Plutarch took up the theme in a lively dialogue that was later to have several imitators. Contained in his 1st-century Moralia is the Gryllus episode in which Circe allows Odysseus to interview a fellow Greek turned into a pig. There his interlocutor informs Odysseus that his present existence is preferable to the human. They then engage in a philosophical dialogue in which every human value is questioned and beasts are proved to be of superior wisdom and virtue.