Descriptions of the Exmoor Beast indicate that it is a large, cat-like animal, either black or dark gray. It has a long tail and stands low to the ground. John Milton reported dark green eyes as the cat ran across the road in front of his car. The "cat" has also been known to jump 6 foot high fences.

Investigations of the Exmoor creature have ruled out all possible theories including foxes or wild dogs. The way in which sheep and other domestic animals have been killed suggest that a large cat was responsible. Cats attack at the neck of their prey, often breaking it, or tearing out the throat. Dogs, on the other hand, attack from all angles including the back and legs. Foxes are unlikely predators of sheep because they are too small and lack the strength to bring down a comparatively large animal. The problem with the cat theory is that there are no native big cats in the Exmoor region of England.

Those who have researched the Exmoor Beast suggest that it is a prime example of micro-evolution. The cats (there appears to be more than one) are believed to be descended from an escaped black puma, which mated with a leopard, and created a new species of cat. Due to the confinement of the gene pool, the rare black colouration of the puma became a "common" trait for the Exmoor cats. Because of the adaptability of pumas, the new species was able to fit in to the non-native environment.