Panoplosaurus mirus is the only species in the genus Panoplosaurus. The species was named in 1919 by Canadian palaeontologist Lawrence Lambe. The name is based on Greek words, and effectively means "completely armoured lizard".

Panoplosaurus mirus weighed about 3.5 t (4 tn.), and was about 4.5 m (15 ft.) long. They were medium-sized animals in comparison to some of their relatives.

Panoplosaurus dinosaurs belong to the group of armoured dinosaurs known as nodosaurs. Dinosaurs in the other group of armoured dinosaurs are called ankylosaurs. In both groups, the upper part of the body was covered with saucer-like, bony plates imbedded in the skin—the "armour". Dinosaurs in both groups had similar body size and proportions.

In a related nodosaurid, Edmontonia, the animal was further protected by a row of great, solid spines located on its flanks. Unlike ankylosaurs such as Euoplocephalus, the nodosaurs did not have tail clubs.

Panoplosaurus has been found only in Late Cretaceous sediments from around 75 million years ago, in Alberta's Dinosaur Provincial Park. Nodosaurids appear to have been confined to western North America, living in coastal plain flatlands near ancient mid-continental seaways. These herbivorous quadrupeds browsed on low-lying vegetation.