Melanion was the son of Amphidamas, a prince of Arcadia, and the brother of Antimache.

His father Amphidamas was the brother of Iasus, who in the Arcadian tradition was the father of Atalanta. This kinship made Melanion and his wife first cousins, establishing his standing within the Arcadian nobility through paternal descent.

Two competing traditions account for the marriage of Atalanta. In the Boeotian version, preserved in the archaic Catalogue of Women, Atalanta would only marry a man who could beat her in a footrace. Hippomenes, though the slower runner, received three golden apples from the love-goddess Aphrodite and dropped them one by one during the race; each time Atalanta paused to gather an apple, Hippomenes gained ground and so won both the race and the marriage. Having failed to properly thank Aphrodite, he angered the goddess, who inspired uncontrollable lust in the pair; they lay together in a sacred temple and were in punishment transformed into lions.

In the Arcadian version, the husband is Melanion. Aristophanes' Lysistrata preserves an image of Melanion as a man who avoided marriage and withdrew to the mountains, hunting wild game with nets he wove and never returning home out of hatred for women. In some versions the Arcadian Melanion supersedes Hippomenes as Atalanta's husband, though his manner of wooing the maiden is often passed over by the ancient testimonies. Rather than winning by the footrace, Melanion functions as a devoted hunter-companion, presenting himself as a kind of male counterpart to Atalanta.

The accounts of Melanion evolve across antiquity. Xenophon reports that Melanion was a pupil of Chiron and won Atalanta with great labour. Ovid and Propertius describe him following Atalanta about, battling wild beasts and carrying her nets while she hunted, and even being wounded by the centaur Hylaeus, an image that emphasizes devotion over competitive victory.

Apollodorus (second century) was the first to name Melanion, rather than Hippomenes, as the winner of the footrace. Palaephatus (fourth century) offers the first known reference to the lion-metamorphosis myth; in his rationalized version the couple enter a lion's den and are killed by the beasts, while onlookers wrongly believe Melanion and Atalanta have been turned into animals.

It has been hypothesized that Atalanta herself is an amalgamation of two heroines — one Boeotian, associated with the footrace myth, and one Arcadian, who hunted the Calydonian Boar alongside Meleager — which would explain the contradictory identities of her suitor. Scholars such as Detienne, Fontenrose, and Forbes Irving disputed the necessity of this theory, noting that both heroines excel in masculine pursuits and that geography is a common point of variation between myths. Conventionally, Hippomenes is the husband in the Boeotian tradition and Melanion in the Arcadian one. Melanion is also named the father of Parthenopaeus, himself an Arcadian native.

According to the traveller Pausanias, a scene on the Chest of Cypselus, dedicated at Olympia, depicted Atalanta holding a deer and standing next to Melanion.

A fragmentary dinos excavated in Athens shows Atalanta in the company of a man whose name begins with the letters "Mel-", identified with Melanion, although Meleager remains another possibility; the fragmentary state of the inscription prevents a certain attribution.