Typhonium is one of the most species-rich genera of Araceae in tropical Asia, with north-eastern Thailand representing an important but still incompletely documented area of diversity. During botanical surveys in northeastern Thailand, an unusual population of Typhonium was discovered in mixed deciduous forest and dry evergreen forest at 300–400 m elevation. Detailed morphological study of living plants and herbarium specimens, together with comparisons with relevant protologues, regional floras, and recently described species, confirmed that this population represents a species new to science. It is here described as Typhonium mukdahanense Chatan & Promprom, sp. nov. The new species is morphologically most similar to T. fornicatum, but differs by its taller habit, larger hastate to trisect leaf blades, more numerous primary lateral veins, larger and nearly symmetrical spathe tube, triangular reflexed spathe limb, dark red stigma with a cream-colored depressed center, sterile interstice bearing 10–14 staminodes arranged in two whorls, slightly curved and not spreading–declinate appendix, and pyriform mottled berries. It also differs from T. acetosella by its broader leaf blades, reflexed triangular spathe limb, dark red stigma, and pyriform fruits. The new species is currently known only from the type locality and is therefore provisionally assessed as Critically Endangered (CR) according to the IUCN Red List Categories and Criteria. A detailed description, diagnosis, information on distribution, habitat, phenology, conservation status, and an identification key to morphologically similar species are provided.