Chesnaught is a bipedal, mammalian Pokémon with some plant-like features. It possesses a prominent domed, armor-like shell similar to that of a chestnut. The armor is pale beige in coloration with four large spines jutting out of the back. The armor is trimmed with red and green bands, with the green on the outermost edge. There is an additional spine protruding from the armor over each of Chesnaught's shoulders, which are connected by a green breastplate. Its body is colored similarly to the shell, and its long limbs and tail are banded with plates of armor. The top surfaces of the tail and arms are protected by green armor, and the arms have two small spines. It has three brown, clawed digits on its hands and feet. Its hands can fuse together to create a spike-covered "shield". Chesnaught has fluffy white fur on its belly and fringing its face like a beard. It has a small, pink nose with a three-pointed patch of brown fur extending up its short snout. It also has four pointed teeth and a plate of beige armor atop its head, similar to a helmet.
Chesnaught is renowned for its tank-like body; it is capable of throwing a Tackle that can flip a 50-ton truck. Once it gets into its defensive stance with its hands covering its face, it can stand up to a bomb's explosion. It will not hesitate to use its sturdy body to shield its allies from danger. Chesnaught is capable of learning Spiky Shield, its former signature move.