Philonoe was born in Xanthus, the capital city of Lycia, the great kingdom in southwestern Asia Minor whose wealth came from the fertile valleys between the mountains and the sea. Her father was Iobates, the king who ruled from a palace famous for its gardens and its treasuries, and her mother was one of the noblewomen of the Lycian court. She had at least one sister, Anteia, who had married Proetus, the king of Tiryns in Argos, and who lived across the Aegean Sea in the palace of the Greek mainland. Philonoe grew up in the luxury of the Lycian court, trained in the arts of a princess, and waited for the day when her father would choose a husband worthy of her hand. She did not know that the man who would claim her would arrive as a condemned murderer, bearing a letter that demanded his own death.

The man was Bellerophon, a Corinthian prince of divine blood, the son of Glaucus and the grandson of Sisyphus, or in some accounts the son of Poseidon, the god of the sea. He had come to Tiryns seeking purification for a killing, and there Proetus's wife Anteia had fallen in love with him. When Bellerophon refused her advances, Anteia accused him of attempted rape, and Proetus, unwilling to kill a guest under his own roof, sent Bellerophon to Lycia with a sealed letter to Iobates. The letter asked Iobates to put the bearer to death. Iobates, bound by the laws of hospitality, could not kill a man who had come to him as a messenger, and he devised a cunning solution: he would send Bellerophon on tasks so dangerous that the gods themselves would kill him.

The tasks were the most famous in Greek mythology before the labours of Heracles. First, Bellerophon must slay the Chimera, the fire-breathing monster with the head of a lion, the body of a goat, and the tail of a serpent, a creature that had been ravaging the Lycian countryside. Bellerophon tamed the winged horse Pegasus, a gift from Athena, the goddess of wisdom, or from Poseidon, and he flew above the Chimera, driving a lead-tipped spear down its throat so that the monster's own fire melted the lead and choked it to death. Next, Iobates sent him against the Solymi, a fierce tribe that warred with Lycia, and Bellerophon defeated them from the air. Then came the Amazons, the warrior women of Asia Minor, and Bellerophon scattered their army with the same aerial tactics. Finally, Iobates laid an ambush with his best warriors, and Bellerophon survived that too. Iobates understood then that Bellerophon was favoured by the gods, and he welcomed him into the palace not as a condemned man but as a hero.

The reward for the hero was Philonoe. Iobates gave his daughter to Bellerophon in marriage, and the wedding was celebrated with the full splendour of the Lycian court. The marriage was happy and fruitful. Philonoe bore Bellerophon three children: Isander, who would one day be killed by the Solymi in a war of vengeance; Hippolochus, whose son Glaucus would fight as a Lycian ally of the Trojans in the Trojan War; and Laodameia, who would bear Sarpedon, another great Lycian hero, though some accounts make Sarpedon the son of Zeus and Laodameia a different woman. For a time, Bellerophon and Philonoe ruled Lycia together, and their house was honoured across Asia Minor.

But Bellerophon's pride grew with his success. He believed that his divine parentage and his victories entitled him to a place among the gods themselves, and he tried to fly Pegasus to Olympus, the home of the immortals. Zeus, the king of the gods, sent a gadfly to sting the winged horse, and Pegasus threw Bellerophon, who fell to the earth and was crippled or killed, depending on the version. Philonoe survived her husband's fall. In some accounts, she was granted immortality by Artemis, the virgin goddess who admired her virtue and her patience, and she became a companion of the goddess, hunting with her in the forests of Lycia forever. In other accounts, she remained in Lycia as a widow, raising her children and watching her grandsons ride to the Trojan War that her husband had never lived to see.