Deidamia was a daughter of King Lycomedes, who ruled on the island of Scyros, and was one of his seven daughters. She married Achilles and became the mother of Neoptolemus. Following the Trojan War, her son gave her in marriage to Helenus, a Trojan captive.

Alternative traditions complicate this lineage: some accounts make Iphigenia, rather than Deidamia, the mother of Neoptolemus, with Deidamia merely raising the boy. Another tradition credits her with a second son named Oneiros.

Deidamia was one of King Lycomedes' seven daughters among whom Achilles was concealed on Scyros. In some accounts Achilles lived at the king's court disguised as one of the daughters, or as a lady-in-waiting under the name Pyrrha. The two soon became romantically involved, to the point of intimacy. After Odysseus exposed Achilles' true identity at the court, the hero departed for the Trojan War, leaving Deidamia behind.

Years later, Deidamia tried to dissuade their son Neoptolemus from joining his father in the war. After Achilles' death, Neoptolemus went to Troy. After the war, Neoptolemus gave Deidamia in marriage to his slave Helenus, a son of Priam whom he had brought to Epirus. Neoptolemus himself was eventually killed by Orestes.

According to Ptolemy Hephaestion, Achilles and Deidamia had another son, Oneiros, who was killed by Orestes in Phocis while the two were fighting over a place to pitch a tent.

The tragedians Euripides and Sophocles, both of the 5th century BC, each composed a work titled Skyrioi, in which Deidamia was an important figure. In poetry of the Greek Anthology she was sometimes called Pyrrha instead.

An anonymous Latin author of the 11th century created a verse epistle, Deidamia Achilli, in the style of Ovid's Heroides, in which Deidamia complains to Achilles about her abandonment.