The Slaty-headed Longbill has a dark head and a long, strongly curved bill. Records from New Guinea's mountain forests include feeding on nectar and arthropods.
Its head and nape are dark bluish grey, with grey wings and a noticeable yellow throat spot. Females look similar but paler; immature plumage is undescribed.
It is found mainly in primary forest on hills and lower mountains, but also occurs in secondary growth and at garden or forest edges. It usually forages alone in the understory or middle levels, and recorded foods include arthropods and nectar. It makes a neat cup of fine greenish vegetation and fibres, placed in a sapling fork or on a slender branch.
An extinction-risk assessment has not been added yet.