Pittheus was born in the Peloponnese, the great peninsula of southern Greece, the son of Pelops and Hippodamia. His father was the Phrygian prince who had won his mother in a treacherous chariot race and who had founded the Olympic Games upon the grave of the king he had murdered. His brothers were Atreus and Thyestes, the twin seeds of a curse that would destroy the house of Pelops for four generations, producing the tragedies of Mycenae and the war against Troy. Pittheus was different from his brothers. Where they were driven by ambition and rage, he was driven by wisdom and cunning, and he chose to build his kingdom in Troezen, a small city on the eastern coast of the Argolid, facing the island of Aegina across the Saronic Gulf. Troezen was not a great power like Mycenae or Sparta, but under Pittheus it became famous for its justice, its learning, and the wisdom of its king.

Pittheus had a daughter named Aethra, and she was beautiful. Her beauty attracted suitors from across the Argolid, but Pittheus was careful in his choice of a husband. He wanted not merely a strong warrior but a king whose blood would elevate his grandson to the thrones of Greece. The opportunity came when Aegeus, the king of Athens, visited Troezen. Aegeus was a man in distress. He had been married twice, to Meta and Chalciope, and neither union had produced a child. He had consulted the oracle at Delphi, and the priestess of Apollo had given him a riddle rather than a clear answer: "Do not loose the wineskin's foot until you reach the heights of Athens." Aegeus did not understand the prophecy, and on his way home he stopped at Troezen to ask Pittheus, who was famous for his wisdom, to interpret it for him.

Pittheus understood the oracle perfectly. The "wineskin's foot" was a crude metaphor for the male generative organ, and the prophecy meant that Aegeus should not father a child until he returned to Athens. But Pittheus saw an opportunity that the gods themselves had placed in his hands. He invited Aegeus to a feast, filled his cup with wine again and again, and when the king of Athens was drunk beyond resistance, he led him to the bedchamber where Aethra lay waiting. That night, Aegeus lay with Aethra, and from their union was conceived Theseus, the hero who would one day unite Attica under the rule of Athens and become the most famous king in Greek legend. Some accounts say that Poseidon, the god of the sea, also lay with Aethra that same night, so that Theseus had two fathers, one mortal and one divine, and the Greeks debated which was his true sire for centuries.

Before Aegeus left Troezen, he placed his sword and his sandals beneath a heavy rock and told Aethra that when their son was strong enough to lift the rock, he should take the sword and the sandals and come to Athens to claim his inheritance. Pittheus raised the boy in secret, teaching him the arts of war, the laws of the city, and the cunning that had made his own grandfather famous. When Theseus was sixteen, or perhaps eighteen, he lifted the rock with ease, took the sword and the sandals, and set out for Athens by the land route, choosing the dangerous road through the Isthmus of Corinth rather than the safe sea voyage, because he wished to prove himself against the bandits and monsters who infested the road. Pittheus watched him go with a grandfather's pride and a politician's calculation, knowing that if Theseus survived, he would one day rule not only Troezen but Athens as well.

Pittheus's later life is not described in detail in the surviving sources. He seems to have died before Theseus's most famous adventures, the journey to Crete to kill the Minotaur, the war against the Amazons, and the abduction of Helen. But his legacy was secure. The laws of Troezen were famous throughout Greece, and the city remained a place of refuge and wisdom long after his death. The tomb of Pittheus was shown to travellers in the city, and Pausanias, the Greek traveller who wrote his Description of Greece in the second century CE, saw it and recorded that the Troezenians still honoured their wise king as the founder of their constitution. In the end, Pittheus achieved what his more famous brothers could not: he built a kingdom that outlasted the curse, and he placed his grandson on a throne that would shape the destiny of Greece.