We document a ~700 km northward range extension of the rare Andaman grunt, Pomadasys andamanensis McKay and Satapoomin 1994, to the Bangladesh coast of the north-eastern Bay of Bengal. Sixteen specimens (82–129 mm SL) were collected from fishermen catches in Ukhia, Teknaf and Zinjira Island, south-eastern Bangladesh, during 2014–2019 and their counts, measurements and descriptions are provided in detail. In addition, underwater videography (near Zinjira Island), shows an individual swimming over sand-gravel-rock bottom covered with a dense bed of brown algae, predominantly Padina and Dictyota. Using the Cytochrome Oxidase subunit I (COI) region sequence variation of mitochondrial DNA, four specimens were found genetically indistinguishable from the topotype (Andaman Sea coast of Thailand) specimens collected in this study. Long regarded as an endemic species to the Andaman Sea (type locality), the distribution range of P. andamanensis now extends from Phuket Island in the south to the Inani Coast in Cox’s Bazar, Bangladesh in the north, spanning roughly 1500 km in the Andaman Sea and eastern Bay of Bengal. Comparison between published COI barcode data of P. andamanensis and the barcodes generated in this study indicates the presence of a cryptic sibling species from southern Bali, Indonesia, in the southwestern end of the Coral Triangle. A deeper phylogenetic and taxonomic investigation covering more Pomadasys spp. in the Bay of Bengal and neighboring region is suggested to resolve species level ambiguities.