A new species of the genus Mesomeloe (Meloidae) is described from Qatar on the north-eastern coast of the Arabian Peninsula. Mesomeloe ottomerkli sp. nov., which is currently only known from the type locality, was previously identified as Meloe (Mesomeloe) coelatus. Both the morphological and molecular variability of M. coelatus across its wide distribution range are studied to determine the level of congruence between the morphological and genetic differentiation of M. coelatus and the new species. Mesomeloe ottomerkli is distinguishable from all other congeneric species in various traits: it presents a body tegument and appendages that are black in colour and shiny in appearance; an elytral surface absent of impressed longitudinal shallow ridges; a pronotal surface absent of depressed areas and longitudinal midline; and a pronotal base that is slightly arcuate. In addition, males of M. ottomerkli have antennae that gradually widen towards the apex; protarsomeres with a brush patch of yellowish setae on the ventral surface of the first two segments; genitalia in which the gonostyli, in lateral view, become slenderer towards the apex and an aedeagus that is relatively wide and rounded in the distal portion. The distribution records of M. coelatus are also updated and summarized.