Here we describe a new phocid, Hadrokirus martini gen. et sp. nov., from the Pisco Formation, in the locality of Sud-Sacaco (Late Miocene to Early Pliocene of Peru). This taxon is the third true seal described from this locality. It is characterized by strong dentition paired with a powerful masticatory musculature and a peculiar atlas. No precise diet is inferred here, but a propensity for durophagy and predation on large prey (such as the extant leopard seal, Hydrurga leptonyx) can be considered. A cladistic analysis including characters from the literature as well as original ones places Hadrokirus among lobodontines in a clade with Piscophoca pacifica, another phocid from the Pisco Formation. In addition, this analysis supports the monophyly of both Phocinae and Monachinae and recognizes a clade consisting of the four extant species of lobodontines, with Acrophoca longirostris (the third phocid from the Pisco Formation) as sister-group of this clade. All clades are supported by unambiguous non-homoplastic synapomorphies. Following the optimization, our analysis recognizes aquatic innovations as phocine reversions at the scale of Carnivora, or as convergences of monachines with non-phocid pinnipeds.