Nyctibatrachus mewasinghi was described in 2017 by the herpetologist Keerthi Krutha and her colleagues based on an adult female specimen collected from the village of Peruvannamuzhi in the Malabar Wildlife Sanctuary in the state of Kerala.

The side of the body is slightly lighter than the back, and the underside is mainly off-white, with some scattered greyish-brown spots on the throat.

When preserved in 70% ethanol, the frog has a more faded colour and the bands along the back are cream to light brown.

[3] N. mewasinghi can be distinguished from its congeners by a combination of its small snout–vent length; the head being almost as wide or slightly wider than it is long; a prominent Y-shaped ridge from the upper lip to the nostrils; weakly wrinkled skin on the upper sides with prominent granular projections; the absence of glandular folds on the sides of the back; the presence of the dorso-terminal groove (groove on the upper side of the tip of the digit) on the third finger and fourth toe; the discs on the third finger and fourth toe being well-developed and slightly wider than the finger and toe, respectively; two tubercles on the palm; small webbing; the thigh being almost as long as the lower leg; and the lower leg being almost as long as the foot.

[3] N. mewasinghi is endemic to the Western Ghats of India, where it is known only from the Malabar Wildlife Sanctuary in Kerala, north of the Palakkad Gap.

The specimens used to describe the species were collected from a stream with plant cover, running alongside a wall ahead of a drain releasing excess water from the Peruvannamuzhi Dam, and were at an elevation of 38 m (125 ft).