The black-naped monarch is a small passerine bird that is typically found in southern and south-eastern Asia. It is known for its bright blue plumage, with males having a distinctive black patch on the back of their head and a narrow black half collar, while females are duller with olive brown wings and lack the black markings on their head.

This species has a call that is similar to that of the Asian paradise flycatcher, and in tropical forest habitats, pairs may join mixed-species foraging flocks. The black-naped monarch breeds across tropical southern Asia from India and Sri Lanka east to Indonesia and the Philippines, and is usually found in thick forests and other well-wooded habitats. Although they are largely residents, local seasonal movements are known.

During the breeding season in India, which is from March to August, the black-naped monarch builds a neat cup nest placed in a fork. The cup is lined with filaments of webbing and fungi, including those of the genus Marasmius which are known to produce antibiotics and may benefit the birds by protecting the young from infection. The nest is built by the female while the male guards. The typical clutch is three eggs, which both parents incubate and both feed the young, which hatch after about 12 days. The webs of large spiders such as Nephila maculata have been known to trap the bird.

This species is insectivorous, often hunting by flycatching, and typically sits very upright whilst perched prominently, like a shrike. When alarmed or alert, the nape feathers are raised into a pointed crest. They join mixed-species foraging flocks, being among the most significant members of such flocks in the Western Ghats, and are active in the understory of forest canopies. A study in Sri Lanka showed that they are affected by human disturbance causing them to recede from disturbed edges by about 75 m.

Alternate names for the black-naped monarch include black-naped blue monarch and black-naped monarch flycatcher. Some authorities separate two former subspecies, H. a. blasii (Banggai Island) and H. a. puella (Sulawesi), and place them as subspecies of the pale-blue monarch (Hypothymis puella).

Overall, the black-naped monarch is a fascinating bird that is known for its distinctive appearance and intriguing behavior, making it a subject of interest for bird enthusiasts and researchers alike.