Deinonychus ranged from 2.5-3.0m from snout to the tip of the tail and stood 1.5m high. It weighed between 50-80kg when full grown (Wilfred, 1985), and was robustly built with long forearms that contained three fingers each armed with an especially sharp claw (McGowan,1991). By looking at the structure of the forelimb and hands it is evident that Deinonychus was an obligatory biped. Meaning that even if it had wanted to, Deinonychus could not have walked on all fours.

Deinonychus had an erect posture, where its legs were held beneath the body, much like that of an ostrich. Its trunk was held in a near-horizontal position, neck curving upwards and a tail sticking straight out behind (Wilfred, 1985).