The latest Cretaceous Phosphates of Morocco preserve the highest biodiversity of mosasaurid squamates anywhere in the world. Intensive sampling over the past century has uncovered at least ten genera and thirteen species from the mosasaur subgroups Halisauromorpha, Plioplatecarpinae, and Mosasaurinae. Notably missing from the assemblage are members of the macropredatory Tylosaurinae. The Tylosaurinae were globally rare in the Maastrichtian and their apparent absence has been previously explained by either collecting bias, ecological preference for deeper waters, or habitat restriction to higher paleolatitudes. Here, we describe a new tylosaurine mosasaurid, Hainosaurus boubker sp. nov., based on several partial skulls and isolated teeth originating from the Couche III layer of the Sidi Chennane Phosphate quarry near Oued Zem, Morocco. It is unique amongst tylosaurine mosasaurids in possessing blade-like teeth that are laterally compressed, encircled by enamel facets, and differentiated along the dental margin. The discovery of this new taxon in the Maastrichtian of Morocco is remarkable as it represents both the youngest species of Tylosaurinae and the first occurrence in North Africa.