Leyesaurus is known from the holotype PVSJ 706, a nearly complete skull with articulated mandible and some postcranial remains (vertebral column, scapular and pelvic girdles and hindlimb). The skull has a length of 18 centimeters, and Leyesaurus has been estimated to have been about 2.5 m (8.2 ft) in length. It was collected from the uppermost part of the Quebrada del Barro Formation of the Marayes-El Carrizal Basin, dating to the Lower Jurassic (based on the presence of a massospondylid like Leyesaurus within the formation). Leyesaurus was found near the locality Balde de Leyes, in the Caucete Department of San Juan Province. Within Massospondylidae, Leyesaurus was found to be most closely related to Adeopapposaurus.