The Black-naped Monarch is a slim and agile passerine bird belonging to the family of monarch flycatchers. They are sexually dimorphic with males having a distinctive black patch on the back of the head and a narrow black half collar while the female is duller and lacks the black markings. They have a call that is similar to that of the Asian Paradise Flycatcher and in tropical forest habitats pairs may join mixed-species foraging flocks. Populations differ slightly in plumage color and sizes.
The adult male Black-naped Monarch is 15 cm long, and is mainly pale azure blue apart from a whitish lower belly. It has a black nape and a narrow black gorget. The female is duller and lacks the black markings. Her wings and back are grey-brown. There are however several geographically separated breeding populations that differ in the extent and shade of markings.