Gallardosaurus was found in middle-late Oxfordian-age (Late Jurassic) rocks of the Jagua Formation of western Cuba.

In 1996, Dr. Manuel Iturralde-Vinent and Mark Norell initially mentioned specimen MNHNCu P3005, a partial skull and mandible with a few cervical vertebrae, as resembling that of the species Pliosaurus ferox.

The specimen had been discovered in 1946 by Cuban farmer Juan Gallardo about 8 kilometres (5.0 mi) east of Viñales, Pinar del Río, northwestern Cuba.

Also known from the Jagua Vieja Member are ichthyosaurs, the marine turtle Notoemys oxfordiensis, and the plesiosauroid Vinialesaurus caroli.

The water depth was shallow, perhaps 10 to 12 metres (33 to 39 ft) deep, and oysters and algae colonized the sea bottom.