Adults are 18 cm (7.1 in) long on average and weigh 25–40 g (0.88–1.41 oz), and are mainly green in color, with a red underside and narrow yellow streaking on the cheeks.

Breeding takes place in October; nests are made in holes in tall trees and contain two eggs.

The orange-billed lorikeet was formally described as a species by the German ornithologist Ernst Hartert in 1896 based on specimens from the "Victoria district" in the Owen Stanley Range in New Guinea.

[2] It is treated as having one subspecies by the International Ornithologists' Union;[6] however, some authorities recognize as many as three subspecies on the basis of differences in appearance, with populations from central western New Guinea separated as N. p. alpinus[a] and populations from northeastern New Guinea separated as N. p.

It and the yellow-billed lorikeet are basal within a clade (group of organisms descending from a common ancestor) formed by Neopsittacus, Lorius, Psitteuteles, Parvipsitta, Pseudeos, Chalcopsitta, Glossoptilus, Glossopsitta, Saudareos, Eos, and Trichoglossus.

[7] Adults are mainly dark emerald green, with red underparts and narrow yellow streaking on the cheeks.

[2][7] Vagrancy at lower elevations suggests that the species may sporadically migrate altitudinally;[7] Neopsittacus is one of only five genera in the order Psittaciformes to evolve to be nomadic.

Plants it is known to feed upon include the seed cones of Papuacedrus papuana and the berries of Sericolea pullei.

[7] The orange-billed lorikeet is parasitised by a variety of insects, including the rhinonyssid mites Mesonyssus alisteri and Tinaminyssus trichoglossi,[14][15] the philopterid chewing louse Psittaconirmus zinki,[16] and the menoponid chewing louse Eomenopon semilunare.