Melanochelys trijuga has an elongated carapace, initially somewhat depressed in juveniles, tricarinate, with slightly reverted lateral margins and a feebly serrated posterior margin in the young. The small head has a short snout, and the upper jaw is notched at the middle, with the skin on the posterior part divided into large shields. The carapace is dark brown to blackish, and the plastron is usually dark with a yellow margin, which may be absent in aged specimens. The head is grey-black, occasionally spotted with yellow, and the nuchal shield is moderately small, while vertebral shields exhibit variable shapes.