Ornitholestes was a "lizard-hipped" dinosaur with light, hollow bones. It was an agile two-legged predator and its long tail gave it great manoeuvrability and balance for hunting. Its head was relatively small and short with sharp, conical teeth and a little crest on the top of its nose.

It was small enough to live deep in the forest, where it fed on lizards, small mammals and carrion. It could grab these with its strong hands that had 2 long clawed fingers and one short one.

Ornitholestes was a close relative of Coelophysis. It was also very closely related to the evolutionary line that produced the birds. It had wrists that allowed it to tuck its hands up close to its body in the same way a bird holds its wings.

A partial Ornitholestes skeleton that included the skull and jaw was discovered in 1900 at Bone Cabin Quarry in the Morrison Formation of Wyoming, USA. This is the only specimen apart from an incomplete hand from another individual.