In a genomic study by Chan and colleagues, pit-vipers of the Trimeresurus erythrurus – purpureomaculatus complex from the Ayeyarwady and Yangon regions in Myanmar were demonstrated to be a distinct species based on robust population genetic and species delimitation analyses. Here, we provide morphological characterizations and a formal description of those populations as a new species. The new species, Trimeresurus ayeyarwadyensis sp. nov., is most closely related to T. erythrurus and T. purpureomaculatus and shares morphological characteristics with both of those species. Some specimens of T. ayeyarwadyensis sp. nov. have green dorsal coloration and no distinct dorsal blotches (a trait shared with T. erythrurus but not T. purpureomaculatus ), while others have dark dorsal blotches (a trait shared with T. purpureomaculatus but not T. erythrurus ). The distinct evolutionary trajectory of the new species, coupled with the lack of obvious morphological differentiation, represents a classic example of the cryptic nature of species commonly found in the Trimeresurus group of Asian pit-vipers and underscores the need for data-rich analyses to verify species' boundaries more broadly within this genus.