We describe the first new rodent species from Solomon Islands in more than 80 years. This new giant rat is known from a single specimen captured in a commercially felled Dillenia salomonensis tree on Vangunu Island. Morphologically, it closely resembles a fascinating secondary radiation of 3 species of Uromys (Cyromys) that are endemic to Guadalcanal Island. The cranium can be readily distinguished from those of other species of Uromys by its shorter maxillary tooth row, and shorter incisive foramina. The existence of this species has been suspected for over 2 decades. It is rare and cryptic, and conservation status is Critically Endangered due to its small distributional range, apparent low population densities, and rapid progress of commercial logging on Vangunu Island. Further surveys to locate additional animals and support for community led conservation initiatives on Vangunu are urgently needed to safeguard the species.