The Tasmanian devil has a thick-set, squat build, with relatively large broad head (with powerful jaws and strong teeth) and a short, thick tail. The Tasmanian devil is the size of a small, stoutly-built dog (head/body length about of about 2.15 ft / 65 cm). The fur is mostly or wholly black, but white markings often occur on the chest, rump and shoulders.

The devils have a lot of long whiskers. They are positioned in clumps far back on the top of the head plus in the normal 'whiskery' places. These long whiskers help foraging in the dark.

The skull is short, broad and flattish above with all the teeth crowded together giving the mouth a “full” and powerful look. The upper incisors are long and the canines short and heavy, the first three (of the four) molars are triangular in shape. Devils have jaws of biting power as strong as a dog about 4 times their weight. So a 22 lb / 10 kg devil has as powerful a bite as a 88 lb / 40 kg dog. In this respect they are very similar to hyenas.

Their hearing is excellent. It seems to be the dominant sense. Like most nocturnal animals their sight seems to be oriented heavily on black and white vision, and black and white vision is mainly designed to detect movement. So if something moves they have good eyesight whereas if something stays still they are unlikely to see it clearly. They seem to have an excellent sense of smell, although it is probably not as good as a scent hound.

On rough terrain devils can run faster than a person; on very smooth terrain they cannot run as fast as a good human runner. Devils have been 'clocked' running on a flat road at nearly 15 mph / 25 km/h for up to 0,6 mile / 1 km. Devils can run at 6mph / 10 km/h for many miles / kilometers.

Devils produce a strong, unpleasant odour when under stress, but, when calm and relaxed, they are not smelly, and are clean, tidy animals.

When the devils are very excited, they hold their tail up to demonstrate to other devils that they mean business. When they are very angry they will hold their tail almost straight up.

Devils carry a number of internal and external parasites. They often have small numbers of ticks, tapeworms, and other parasites.

Devils can swim very well. However if they have young in the pouch they avoid swimming for more than very short distances. Devils actually love water and will wade and splash about, even sitting or laying down in it to cool. They will often dabble in water with their front paws, somewhat in the manner of racoons.