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.

The black-naped monarch was described by the French polymath Georges-Louis Leclerc, Comte de Buffon in 1779 in his Histoire Naturelle des Oiseaux.

[2] The bird was also illustrated in a hand-coloured plate engraved by François-Nicolas Martinet in the Planches Enluminées D'Histoire Naturelle which was produced under the supervision of Edme-Louis Daubenton to accompany Buffon's text.

[4] Buffon specified that his specimen had been collected in the Philippines, and in 1939 the American ornithologist James L. Peters restricted the type locality to Manila on the island of Luzon.

[10] Twenty-three subspecies are recognized:[8] The adult male black-naped monarch is about 16 cm long, and is mainly pale azure blue apart from a whitish lower belly.

The Indian peninsula has subspecies H. a. styani (which subsumes H. a. sykesi of Stuart Baker[11]), in which males have very distinct black markings and a whitish abdomen.

[12] The black-naped monarch breeds across tropical southern Asia from Iran and Sri Lanka east to Indonesia and the Philippines.

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.