The black backed forktail is solitary, but is occasionally found in pairs or in family groups.

The bird breeds between March and June, building a nest of plant matter in holes or crevices in rocks and dead trees.

British naturalist Brian H. Hodgson scientifically described the black-backed forktail in 1836, from a specimen obtained in Nepal.

The crown and mantle are completely covered in black feathering, which extends down to the upper forehead, face, scapulars, throat, and sides of the neck.

Juveniles have a white spot behind the eye, and may have dark scales or speckles on its flanks, breast, and belly.

The tail of the juvenile is usually shorter, while the mandible is yellowish, and the maxilla have whitish cutting edges.

[6][5] The bird is similar to the slaty-backed forktail, but lacks the slaty back of the latter, and is also smaller in size.

It also makes a call similar to that of the slaty-backed forktail, described as being reminiscent of a squeaky hinge.

[7] The species is solitary, or occasionally found in pairs, but may be seen in family groups during the breeding season.

Described as a shy bird, it often bobs its tail when feeding, and when at rest opens and closes it with a scissor-like motion.

[6] It habitually flies along the course of a river or stream,[8] and its flight is described as quick and straight, occasionally undulating slightly.

It typically forages along fast-moving streams and rivers, including on rocks in midstream, and may occasionally enter the water.

The nest consists of a cup constructed of plant matter, including dried leaves, moss, and fibres, sometimes lined with leaf skeletons.

[6] Though the species is largely sedentary, first-year birds disperse from their parental breeding areas between April and October.

[9][7] The western end of the species's range is in Garhwal, in the northwest portion of the Indian state of Uttarakhand.

The range extends from there through western and central Nepal to Bhutan and the northeastern Indian states, including Sikkim, Assam, Meghalaya, Arunachal Pradesh, Nagaland, and Manipur.

[11] In 1998 the species was recorded at 2,600 metres (8,500 ft) above sea level in Eaglenest Wildlife Sanctuary in Arunachal Pradesh.

These estimates have led to its being classified as a species of Least Concern by the International Union for Conservation of Nature.