The description of a new cryptic member of the mangrove monitor (Varanus indicus) (Daudin, 1802) group from Indonesia presents a refinement of the systematic concept for a polytypic complex of closely related species. The new species is recognised on the basis of morphological and molecular evidence. It is so far known only from the type locality, the remote Talaud Islands, located between Sulawesi, Halmahera and Mindanao at the outer boundary of the Wallacea transition zone between the Oriental and Australian faunal regions. While the descriptions of several sibling and mostly sympatric species within the last 15 years have not affected the range of V. indicus, here, we demonstrate that morphologically distinct island populations represent independent evolutionary lineages and warrant specific recognition as distinct species within an evolving superspecies complex. In addition, some basic natural history information is provided for the new species based on observations at the type locality. These systematic and zoogeographic investigations reveal shortcomings in the current knowledge concerning the diversity and endemism of Indo-Australian monitor lizards, particularly within the Wallacean region.