Rhacophorus baluensis was originally described from Bundu Tuhan, Gunung Kinabalu, Sabah. Its distribution encompasses Sabah, northern Sarawak, and northern Kalimantan. This tree frog inhabits submontane and montane forests at elevations of approximately 1000–1500 m a.s.l. The photograph by Chien C. Lee documents the species from Kalimantan Timur.

This is a mid-sized frog (50–65 mm snout–vent length) with a relatively robust build. The head is comparatively large and broad. The snout is pointed and projects beyond the lower jaw in lateral view. The canthus rostralis is distinct, and a thin, straight supratympanic fold is present. The eardrum is visible but only indistinctly separated in coloration from the surrounding skin. Skin ridges are present along the outer sides of the forearm and foot. A weak ridge of white tubercles occurs just above the anus, and the heel bears a fleshy spur. The fingers are half-webbed at most, whereas the toes are fully webbed. All digits terminate in large adhesive pads. The dorsal skin is smooth and finely pebbled, while the belly is coarsely pebbled. The pupil is elliptical and horizontally oriented. 

Coloration is generally reported as various shades of brown, sometimes tending toward beige or reddish brown. Individuals can change color depending on stress levels and between day and night. Irregular dark markings on the back are common. Cross-bars on the dorsum and upper surfaces of the limbs may be distinct or faint. The iris is pale golden, sometimes with a darker reddish-brown ring around the pupil in certain populations.

Individuals of this species are not frequently encountered, likely because they spend most of their time high in the forest canopy. When found, they typically occur in low numbers. Inger et al. (2017) described the call as a deep rattle resembling a woodpecker pecking on a hollow tree.

Tadpoles grow large, exceeding 60 mm in total length. The head and trunk are broad and massive. The tail comprises roughly two thirds of the total length and ends bluntly. Tadpoles are brown dorsally, lacking conspicuous patterning, while the belly is greyish and opaque.