The iconic tyrannosaurids were top predators in Asia and North America during the latest Cretaceous, and most species had deep skulls that allowed them to generate extreme bite forces. Two unusual specimens of Alioramus from Mongolia seem to indicate a divergent long-snouted body plan among some derived tyrannosaurids, but the rarity and juvenile nature of these fossils leaves many questions unanswered. Here, we describe a remarkable new species of long-snouted tyrannosaurid from the Maastrichtian of southeastern China, Qianzhousaurus sinensis. Phylogenetic analysis places Qianzhousaurus with both species of Alioramus in a novel longirostrine clade, which was geographically widespread across latest Cretaceous Asia and formed an important component of terrestrial ecosystems during this time. The new specimen is approximately twice the size as both Alioramus individuals, showing that the long-snouted morphology was not a transient juvenile condition of deep-snouted species, but a characteristic of a major tyrannosaurid subgroup.