Billfishes (Perciformes, Xiphioidei) are large marine teleosts characterized by an elongate rostrum formed primarily by greatly lengthened premaxillae. The billfish fossil record extends back to the late Paleocene, but is almost completely dominated by Northern Hemisphere finds despite the wide occurrence of several extant billfish species in southern seas. We report on an associated partial skeleton of a large billfish from upper Oligocene marine deposits on the South Island of New Zealand, described here as Aglyptorhynchus hakataramea, sp. nov. The material is assigned to Aglyptorhynchus—a genus previously known from the mid-Cenozoic of Europe and both the Atlantic and Pacific coasts of the U.S.A.—primarily on the basis of the ventrolaterally expanded flanges on its enlarged maxillae, diagnostic for the genus. It is recognized as a new species owing to its rostral proportions, and lower jaws that do not extend as far anteriorly as the tip of the rostrum as in other Aglyptorhynchus species. The new species is the most complete and informative fossil billfish described to date from the Southern Hemisphere.