We re-describe the holotype and referred specimen of Prosqualodon australis, from the early Miocene of Gaiman Formation (Chubut Province, Argentina), and analyse its phylogenetic position. Our study shows that this taxon is presently represented by an adult and a juvenile individuals and we provide the first diagnosis of the species based on the morphology of the anterior projection of the antorbital process along with plesiomorphic dental features (such as well-marked heterodont teeth, with posterior double rooted teeth in the maxilla, large, lateromedially compressed teeth with long crowns and denticulated enamel). The total body length of P. australis is estimated to be 2 m in the juvenile and 3 m in the adult specimen. We included for the first time this species in a phylogenetic analysis as an operational taxonomic unit itself, recovering P. australis as a stem-odontocete and Prosqualodon as a paraphyletic genus.