We describe a new species of New Guinea vermivorous snake (Toxicocalamus) from a single specimen collected at Wangbin in the Star Mountains, Western Province, Papua New Guinea. The new species is the largest known member of the genus and can be differentiated from all other Toxicocalamus by a combination of the following characters: large size (total length of the holotype 1,200 mm), dorsal head scutes in the typical “colubrid-elapid dorsal nine-scute arrangement”; separate, single preocular and paired postoculars; single anterior temporal and single or paired posterior temporals; six supralabials, with third and fourth supralabial contacting the orbit; dorsal scales in 15–15–15 rows; 203 ventral scales, 29 subcaudal scales; and a divided anal plate. Its erstwhile status, misidentified as Micropechis ikaheka in the collection of the Museum of Comparative Zoology, demonstrates the need for detailed examination of existing collections and is indicative of hidden diversity yet to be identified, not only in the field but also on the shelves of museum collections. We also provide a revised key to the genus Toxicocalamus.