In total, two partial skeletons are known (a fractured skull and parts of two postcranial skeletons, among which paratype MACN CH 895) and is the most completely known theropod from the Middle-Late Jurassic Period of the Southern Hemisphere. "Piatnitzkysaurus" was a relatively lightly built medium-sized bipedal carnivore that was around long and around in mass, though such estimates apply to the holotype, which is a subadult. It had robust arms and powerful hind legs with four toes on each foot. Its ischium is long. Its braincase resembles that of another megalosauroid, the megalosaurid "Piveteausaurus" from France.