Iphicles was born in Thebes, the great city of Boeotia in central Greece, on the same night that Heracles was born, though the two boys were only half-brothers. Their mother was Alcmene, the daughter of Electryon, the king of Mycenae, a woman of such beauty and virtue that Zeus himself desired her. On the night that Amphitryon, Alcmene's husband and the exiled prince of Tiryns, returned from a victorious campaign against the Teleboans, Zeus took his form and lay with Alcmene, extending the night to three times its normal length so that he might enjoy her fully. When Amphitryon returned home in the morning, confused by his wife's coldness, he learned from the seer Teiresias that a god had preceded him. That same night, Amphitryon also lay with Alcmene, and from these two unions on the same night were born two sons: Heracles, the son of Zeus, and Iphicles, the son of Amphitryon. The infants shared a cradle, and the Greeks said that when the serpents sent by Hera, the jealous queen of Olympus, crawled into their bed, Heracles strangled them both while Iphicles screamed in terror, the first and most telling difference between the divine and the mortal.

Iphicles grew up in Thebes under the protection of his uncle Creon, the king who had given his daughter Megara to Heracles in marriage. While Heracles was driven mad by Hera and killed his wife and children, Iphicles survived the disaster and married a woman named Automedusa, or in some accounts Pyrrha, and from this union was born Iolaus, the boy who would become Heracles' most faithful companion. Iolaus loved his uncle with a devotion that surpassed ordinary family affection, and he served as Heracles' charioteer, his squire, and his armour-bearer through every labour and every campaign. Iphicles watched his son ride away with the demigod and must have known that Iolaus would find a glory that he himself could never achieve, for Iphicles was mortal in a way that Heracles was not, and mortality in the company of divinity is its own kind of obscurity.

The defining episode of Iphicles's life was his service alongside Heracles in the wars that the demigod waged across the Greek world. When Heracles led an army against Troy in the generation before the Trojan War that the world remembers, Iphicles was among the companions who sailed with him. This first sack of Troy was punishment for King Laomedon, who had cheated Poseidon and Apollo of their wages and who had broken his word to Heracles by refusing to give him the divine horses he had promised in exchange for rescuing Hesione from the sea monster. Heracles gathered a fleet of six ships and a band of volunteers, and Iphicles stood among them, a mortal man fighting beside a son of Zeus. They stormed the city, slew Laomedon and all his sons except Priam, and sacked Troy long before Agamemnon's thousand ships ever reached its shore. Iphicles fought in that battle not as a hero but as a soldier, one name among many, and the poets who sang of the first sack remembered Heracles and forgot the rest.

Iphicles also fought in the campaign against Oechalia, the city of Eurytus, the archer king who had refused to give his daughter Iole to Heracles after the hero had won an archery contest fair and square. In some accounts, Iphicles died in this war, struck down by the arrows of the Molionidae, the twin sons of Poseidon who fought for King Augeias of Elis, or by some other enemy in the confused fighting that surrounded Heracles's many campaigns. In other traditions, he lived to an old age and died peacefully in Thebes or Tiryns, his death unmarked by omens and his funeral uncelebrated by poets. The uncertainty of his end is itself a comment on his place in the myth: the mortal brother of an immortal hero does not need a definite death, because his life was always defined by someone else's story.

The legacy of Iphicles rests almost entirely on his son Iolaus, who became one of the most beloved figures in Greek mythology. Iolaus helped Heracles slay the Hydra, the many-headed serpent that was the second of the hero's labours, by cauterising the necks as Heracles cut off the heads so that they could not grow back. He drove the chariot in every other labour, he fought at Heracles' side in every war, and when Heracles finally died on Mount Oeta and ascended to Olympus as a god, it was Iolaus who lit the funeral pyre. After Heracles' death, Iolaus led the Heraclidae, the descendants of Heracles, back to the Peloponnese to reclaim their ancestral lands, and he founded the city of Sardis in Lydia. The Thebans worshipped Iolaus as a hero, and the tomb of Iphicles was shown to travellers in Boeotia, though no one could say exactly where he had died or what he had done to deserve remembrance except that he had been the father of a great man and the brother of a greater one.