Iphigenia was born to Agamemnon, the high king of Mycenae and leader of the combined Greek forces preparing to sail against Troy, and Clytemnestra, the daughter of Tyndareus, the king of Sparta, and Leda, the queen who was mother to both Helen, the most beautiful woman in the world, and the warrior twins Castor and Pollux. She grew up in the palace at Mycenae, a fortress city in the Argolid, the region of the Peloponnese dominated by the great citadel with its Lion Gate, and she was the eldest of three children, with a sister Electra and a brother Orestes. Her childhood was one of privilege and expectation, the daughter of the most powerful man in Greece, and she was betrothed in her youth to Achilles, the son of the sea nymph Thetis and the mortal Peleus, the hero whose rage would shape the entire Trojan War.

The crisis of her life began when the Greek fleet assembled at Aulis, a port on the eastern coast of Boeotia in central Greece, where the narrow strait between the mainland and the island of Euboea created a natural harbour. A thousand ships lay at anchor, carrying the warriors of every Greek kingdom from Mycenae to Ithaca, from Sparta to Thessaly, all gathered to retrieve Helen, who had been taken to Troy by the Trojan prince Paris. But the winds were dead calm, and the fleet could not sail. The seer Calchas, the same prophet who had read the omens at Aulis, declared that Artemis, the virgin huntress and goddess of the wild, was angry with Agamemnon. In one version, Agamemnon had killed a stag in a grove sacred to Artemis and then boasted that he was a better hunter than the goddess herself. In another, he had simply offended her by some act of pride. Whatever the cause, Artemis demanded a terrible price: the sacrifice of Iphigenia, Agamemnon's own daughter, before the fleet could receive the winds it needed.

Agamemnon was torn between his love for his daughter and his duty as commander of the Greeks. Menelaus, his brother and the wronged husband of Helen, pressed him to agree, arguing that the honour of Greece and the retrieval of Helen demanded it. Agamemnon sent a message to Mycenae telling Clytemnestra that Achilles wished to marry Iphigenia before the fleet sailed, and that she should bring the girl to Aulis for the wedding. Clytemnestra, overjoyed at the match, dressed Iphigenia in wedding finery and travelled with her to the camp. When they arrived, the truth was revealed. The altar was prepared, the sacrificial fire was lit, and Calchas stood ready with the blade. Achilles, who had known nothing of the deception, was furious and tried to defend Iphigenia, but the Greek army, driven by the desire for war and glory, threatened to stone him if he interfered. Iphigenia, realising that her death was the only thing that would allow the fleet to sail, accepted her fate with a courage that silenced the camp. In some tellings she begged for her life, in others she walked to the altar willingly, declaring that she would die for the glory of Greece.

At the moment the blade fell, Artemis intervened. The goddess snatched Iphigenia from the altar and substituted a deer in her place, or in some versions a calf, so that the Greeks saw blood and believed the sacrifice complete. Iphigenia vanished in a cloud of mist and found herself in Tauris, the land of the Tauri on the northern shore of the Black Sea, in what is now the Crimea. There Artemis made her the high priestess of her temple, but the Taurians practised a brutal cult: every Greek sailor who was shipwrecked on their shores or captured by their warriors was brought to the temple and sacrificed to the goddess, and it was Iphigenia's duty to perform the rites. For years she lived in exile, performing human sacrifices upon her own countrymen, her hands stained with blood that she could not refuse to spill, a priestess of a goddess who had saved her life only to make her the instrument of other deaths.

The turning point came when Orestes, her younger brother, arrived at the temple. Orestes had murdered their mother Clytemnestra in revenge for her murder of Agamemnon, who had been killed on his return from Troy by Clytemnestra and her lover Aegisthus. The Furies, the ancient goddesses of vengeance who pursued those who killed their own kin, had driven Orestes mad, and the oracle at Delphi, the most sacred shrine in Greece, had told him that he could be freed from his torment only if he travelled to Tauris and brought back the sacred statue of Artemis that stood in the temple. Orestes and his faithful companion Pylades, the son of the king of Phocis, were captured by the Taurians and brought to the temple to be sacrificed. Iphigenia, who did not recognise her brother after so many years, prepared them for death according to the ritual, which required that the victims be purified before sacrifice. But in conversation with the prisoners, she learned that one of them was from Mycenae, and when she asked about her family, Orestes revealed his identity. The recognition was one of the most moving scenes in Greek drama: the sister who had been thought dead, the brother who had killed their mother, reunited in a barbarian temple where both were marked for death.

Iphigenia devised a plan. She told King Thoas, the ruler of the Taurians, that the prisoners were unclean and had touched the sacred statue, and that both the statue and the prisoners must be purified in the sea before sacrifice. She persuaded Thoas to allow her to take the statue and the prisoners to the shore. Once there, Orestes and Pylades seized the ship that had brought them, fought off the Taurian guards, and with Iphigenia and the statue aboard, they set sail for Greece. Athena, the grey-eyed goddess of wisdom, appeared to Thoas in a dream and commanded him to let them go, and the king, though furious, obeyed the goddess. Iphigenia carried the statue of Artemis back to Greece and established it at Brauron, the sanctuary in eastern Attica where Artemis was worshipped as the protector of young girls. The cult of Artemis Brauronia became one of the most important religious institutions in Athens, and every year young Athenian girls, before their marriage, dedicated their childhood toys and a lock of hair to the goddess in a ritual called the arkteia, the bear-service, walking in procession to the temple as Iphigenia had once walked to the altar at Aulis.

In some traditions, Iphigenia did not die in Tauris or at Brauron but was made immortal by Artemis and became the goddess Hecate, the deity of crossroads and magic who walked between the worlds of the living and the dead. In others, she lived out her days as a priestess at Brauron, honoured by the Athenians as the woman who had survived the worst the gods could demand and had returned to establish a gentler worship. Her tomb was shown at Megara, and her memory was kept alive in the tragedies of Euripides, who told her story twice: once as the innocent victim at Aulis, and once as the resourceful priestess of Tauris.