Specimens have been measured at more than 8.5m in length, but this is quite exceptional, as 5.5m specimens are already considered large. The body is relatively slim, unlike many other large members of this family. The specific name, amethistina, is an allusion to the milky iridescent sheen on its scales, which gives it an amethyst-like color.

Found in Indonesia (Maluku Islands, Timorlaut Islands, Banda, Kai Islands, Aru Islands, Misool, Selawati, most of Western New Guinea, many islands in Geelvink Bay), Papua New Guinea (including Umboi Island, Bismarck Archipelago, Trobriand Islands, the d'Entrecasteaux Islands to Rossel Island, Louisiade Archipelago), and Australia (on some islands in the Torres Strait, the northern Cape York Peninsula south including the Atherton Tableland and the eastern foothills of the Great Dividing Range). The type locality is unknown. Occurs in both bushland and suburbia. In Indonesia and northern tropical Queensland, Australia, it is found mostly in rainforests. Warm, humid habitats with good water sources are preferred.

The diet generally consists of birds, fruit bats, rats, possums, and other small animals. Larger Australian specimens will catch and eat wallabies, waiting by creek and river banks for prey seeking drinking water.

Common in captivity, but they tend to be snappy.