Hylarana (Indosylvirana) nicobariensis is a slender, long-legged, streamlined brown frog with a long, pointed snout. Adult males and females reach a snout–vent length of about 50 mm. The species is widely distributed on the island of Borneo and occurs throughout much of Southeast Asia; its type locality is Java.

It is common in open habitats and frequently breeds in irrigation ponds or roadside ditches. In many places, it can be considered a commensal species, benefiting from human-altered environments such as agricultural clearings, roadside drains, and irrigation networks. The water bodies used for reproduction may be temporary, filling only during the rainy season, or permanent year-round.

The body is slender and elongated, with a brown base color often shaded by darker tones. A dark to black mask extends from the snout through the eye and continues to the shoulder or even farther along the flank. The snout is distinctly pointed and elongated, and the legs are very long and slender. The toes are extremely long, with slightly expanded tips; webbing covers about half their length, with the fourth toe (the longest) extending well beyond the webbing. The skin on the back is finely pebbled, and a narrow, distinct dorso-lateral fold runs from behind the eye to the groin. Along the upper lip, a sharp white stripe runs beneath the tympanum toward the shoulder. The eardrum is large and distinct, nearly the size of the eye, and darkly pigmented to match the surrounding mask.

During the breeding season, males may gather in large numbers, producing loud choruses that carry across the landscape. Calling males are often hidden among flooded vegetation at the margins of ponds and ditches. Their call consists of several sharp “kek” notes given in rapid succession, sometimes reaching ten in a series.

Tadpoles grow to a total length of about 47 mm. They are generally brown, with pigmentation varying among individuals, and a distinct pattern is often visible along the edges of the tail fins. Tadpoles of H. nicobariensis are sometimes found in the same ponds as those of Hylarana erythraea, indicating overlapping ecological preferences. Although the larvae of the two species are similar in overall shape, they can be distinguished by clear differences in coloration, such as the hue and pattern of the iris.