Telemachus was born in the palace of Odysseus on Ithaca, a rugged island in the Ionian Sea off the western coast of Greece. His father had left for the Trojan War before Telemachus was old enough to remember him, and his mother Penelope had raised him alone, surrounded by the suitors who had come from every noble house in the islands and the mainland to claim her hand. The suitors, led by Antinous and Eurymachus, two arrogant princes from Ithaca itself, had taken over the great hall of the palace, feasting on Odysseus's cattle and wine, slaughtering his sheep and goats, and treating the house as their own. They demanded that Penelope choose a new husband, for Odysseus had been gone twenty years and was presumed dead, but she delayed them with her weaving, promising to choose when her shroud for Laertes, Odysseus's father, was complete, and each night she unravelled what she had woven by day. Telemachus grew up in this atmosphere of tension and humiliation, a boy with a father's name but no father's presence, watching his inheritance disappear bite by bite.

When he was about twenty years old, Athena came to him in disguise. She appeared as Mentor, an old and trusted friend of Odysseus, and she found Telemachus sitting among the suitors in the great hall, his heart heavy with shame and anger. She spoke to him with words that stirred his blood, telling him that he was no longer a child and that it was time for him to act like the son of a great king. She urged him to call an assembly of the Ithacans, to denounce the suitors publicly, and to demand that they leave his house. More importantly, she told him to travel to Pylos, the city of Nestor, the oldest of the Greek heroes who had fought at Troy, and to Sparta, the city of Menelaus and Helen, to ask if anyone had news of his father. Telemachus, inspired by the goddess's words, stood before the assembly and spoke for the first time as a man, condemning the suitors and announcing his intention to sail. The suitors mocked him, but his words marked the end of his childhood.

Telemachus sailed with a small crew to Pylos, the kingdom of Nestor on the western coast of the Peloponnese. Nestor, who was now an old man of great wisdom and even greater verbosity, received the young prince with the hospitality that was sacred to the gods. He told Telemachus what he knew of the Greek heroes after the fall of Troy: how Menelaus and Agamemnon had quarrelled, how Ajax the Lesser had been shipwrecked, how Nestor himself had arrived safely after a long voyage. But he had no news of Odysseus. He advised Telemachus to travel to Sparta and ask Menelaus directly, for Menelaus had wandered the seas for years before returning home and might have encountered Odysseus on his travels. Nestor provided a chariot and his own son Pisistratus as a companion, and Telemachus set out for Sparta, the city of the two kings, Menelaus and his brother Agamemnon, though Agamemnon was now dead, murdered by his wife Clytemnestra and her lover Aegisthus on his return from Troy.

At Sparta, Telemachus was received with royal hospitality by Menelaus and Helen, the most beautiful woman in the world, whose abduction by the Trojan prince Paris had caused the war that had taken Telemachus's father away. Menelaus told the young prince of his own wanderings, of his years in Egypt and Phoenicia, and of how he had learned from the sea god Proteus, the old man of the sea who could change his shape at will, that Odysseus was alive but trapped on the island of Ogygia, held captive by the nymph Calypso, who loved him and would not let him go. This was the first certain news Telemachus had ever heard of his father, and it filled him with a mixture of hope and despair, for Ogygia was far away and Calypso's power was great. Helen, recognising the young man's grief, gave him a robe for his future bride and spoke kindly to him, and Telemachus, with Pisistratus, prepared to return to Ithaca.

While Telemachus was away, the suitors at Ithaca learned of his journey and plotted to ambush him on his return, to kill him at sea and remove the last obstacle to their possession of Penelope and the kingdom. They sent a ship to wait for him at the island of Same, but Athena, who had guided his voyage, warned him of the danger and brought him home by a different route. He arrived at Ithaca to find that a beggar had appeared at the palace, a ragged old man who was in fact Odysseus in disguise, returned from Ogygia and from further wanderings, testing the loyalty of his household before revealing himself. Telemachus did not recognise his father at first, but Athena opened his eyes, and the reunion between father and son, after twenty years of separation, was one of the most moving scenes in all literature. They wept together, and Odysseus told Telemachus of his plans: the suitors would be destroyed, and the palace would be cleansed.

The next day, Penelope announced that she would marry the man who could string the great bow of Odysseus and shoot an arrow through twelve axe heads set in a row. The suitors tried and failed, for the bow was too stiff for any man but its owner. Then the beggar asked to try, and with a single motion he strung the bow and sent the arrow through the axe heads. He cast off his rags and revealed himself as Odysseus, and Telemachus stood beside him with spear and shield. The slaughter that followed was terrible but just. Odysseus, Telemachus, and two loyal servants, the swineherd Eumaeus and the cowherd Philoetius, killed every suitor in the great hall, while Athena held the doors to prevent escape. Telemachus fought with the skill and courage of his father's son, and when the battle was over, the palace was cleansed of the men who had consumed its wealth and dishonoured its queen. The bodies were dragged from the hall, and the house was purified with fire and sulphur.