The Black-billed Weaver lives in dense undergrowth in African montane forest. Male yellow markings vary between its geographically separated forms: the Cameroon form has a yellow breast collar, while the eastern form has yellow on the face.
The bird is black with yellow on the head. Male markings vary by subspecies: the nominate form, including Cameroon, has a yellow breast collar separating the black chin from the rest of the black underparts; the eastern DRC and East African form has a yellow face. In females, yellow extends onto the throat.
It stays low in montane forest undergrowth and dense secondary bush, usually in pairs and sometimes in mixed-species flocks. Its diet includes insects as well as fruits and seeds.
An extinction-risk assessment has not been added yet.