Meristogenys orphnocnemis inhabits rocky streams in lowland and hillside forests of Brunei, Sabah, and northern Kalimantan. The species was described by Matsui (1986), with the type locality at Bundu Tuhan, Kinabalu, Sabah (990 m a.s.l.).

Females grow much larger than males, reaching up to 70 mm in snout–vent length (SVL), whereas males measure approximately 50 mm SVL. Males have a slender body, while females are moderately stocky. The legs are long and slender. The snout is moderately long and projects in profile. The tips of the toes and fingers are expanded into slightly rhomboidal discs. The toes are fully webbed. The skin on the dorsum is finely shagreened, and dorsolateral folds are present.

Dorsal coloration is brown in varying shades, with the back featuring scattered dark and light markings. The upper lip lacks dark markings, lower lip often barred black and white. The dorsal surface of the thigh bears broad bands, while the posterior surface is dark and mottled with light spots. The throat, chest, and belly are white or cream; in males, the throat bears dark lateral vocal sac areas. The iris is golden or bronze in its upper and lower sectors, and reddish in the anterior and posterior sectors.

Meristogenys orphnocnemis is common in lowland and hillside streams. Individuals are most often seen perching on roots, rocks, or soil along the slopes of stream banks. Tadpoles are commonly encountered at night, adhering to rocks and grazing on overflown rock surfaces. The tadpoles are brown or grey above, with dark blotches on the tail and a finer spotted pattern on the head and trunk. The skin of the head and trunk bears tiny spikes. The snout and body are depressed and streamlined, the tail is strong with a pointed tip, and total length can reach approximately 40 mm.