Nestor was born in Pylos, the great city on the western coast of the Peloponnese in the region of Messenia, the son of Neleus and Chloris. Neleus was a son of Poseidon, the god of the sea, and Tyro, the daughter of Salmoneus, and he had founded Pylos after a quarrel with his twin brother Pelias, the king of Iolcus. Nestor grew up in a palace of twelve brothers, all of them proud, all of them warriors, and all of them destined to die before their time. When Heracles, the hero forced to complete twelve impossible labours, came to Messenia in a rage against Neleus, he killed eleven of the brothers and would have killed Nestor too, but Nestor was away from the city, either on a campaign or in hiding, and he survived as the last of the Neleidae, the house of Neleus.

In his youth, Nestor was a warrior of renown. He sailed with the Argonauts, the crew of the ship Argo who sought the Golden Fleece in the distant land of Colchis on the Black Sea, and he fought in the great battle between the Lapiths and the Centaurs, the horse-men who had been born from the cloud-phantom Nephele and who tried to abduct the women at the wedding of Pirithous. In that battle, Nestor killed his share of the monsters and earned a reputation for courage that would last his whole life. But it was not as a warrior that he would be remembered. It was as a speaker, a counselor, a man whose long memory and longer speeches made him the conscience of the Greek camp at Troy.

When the Trojan War began, Nestor was already an old man, past his fighting prime, but he brought fifty ships from Pylos to the muster at Aulis, a contribution that only Agamemnon, Diomedes, and Odysseus could match. At Troy, he did not fight in the front rank as he had in his youth, but he rode his chariot along the lines, encouraging the men, offering advice to the kings, and telling stories of the old days when heroes were stronger and the gods more visible. His most famous characteristic was his garrulity. When Nestor spoke, he spoke at length, weaving his counsel into long narratives of his own youthful exploits, comparing the present crisis to some ancient battle, and drawing out his point with so many digressions that his listeners sometimes forgot what he had been asked. But the advice, when it finally arrived, was always sound.

In the ninth year of the war, when Agamemnon and Achilles quarrelled over the slave-girl Briseis and Achilles withdrew from the fighting in a rage, Nestor tried to mediate. He reminded Agamemnon that Achilles was the Greeks' best warrior and that insulting him was folly. He reminded Achilles that Agamemnon was the commander and that pride was a young man's luxury that an old man could not afford. Neither listened. When Patroclus, the beloved friend of Achilles, came to Nestor's tent to ask what had become of the wounded Machaon, Nestor seized the opportunity to urge Patroclus to wear Achilles's armour and lead the Myrmidons into battle, a suggestion that led directly to Patroclus's death at the hands of Hector. Nestor did not mean to kill Patroclus. He meant to save the Greeks. But his advice, like so much advice from old men to young ones, had consequences that no one could foresee.

Nestor's personal tragedy at Troy was the death of his son Antilochus. Antilochus was the fastest runner among the Greeks after Achilles, a young man of courage and filial devotion who had won the funeral games of Patroclus by a trick of cunning rather than pure speed. When Memnon, the Ethiopian prince who came to Troy as an ally of the Trojans, attacked the Greek camp, Antilochus threw himself between the warrior and his father, taking the blow that was meant for Nestor and dying in his place. Nestor's grief was terrible, and Achilles, who had loved Antilochus, avenged his death by killing Memnon in single combat. But the old king's sorrow never fully lifted, and when he returned to Pylos after the war, he carried with him the memory of a son who had died to save him.

In the Odyssey, Nestor appears as the first host of Telemachus, the son of Odysseus, who has come to the Peloponnese in search of news of his father. Nestor receives the young man with the full ceremony of Homeric hospitality, slaughtering a heifer in his honour, seating him in a chair of honour, and pouring libations to Athena, the goddess of wisdom. But Nestor cannot tell Telemachus what has become of Odysseus. He knows only that the gods scattered the Greek fleet after the fall of Troy, and that he himself reached Pylos safely while others were lost at sea. He sends Telemachus on to Sparta in the chariot of his son Pisistratus, and the scene is one of the most moving in the poem: the old king, surrounded by his surviving sons, offering what comfort he can to a boy who is searching for a father who may never return.