Tandanus bellingerensis, new species, is described based on specimens from four river drainages (Bellinger, Macleay, Hastings, and Manning rivers) of the mid-northern coast of New South Wales, Australia. Previously, three species were recognized in the genus Tandanus: T. tropicanus of the wet tropics region of northeast Queensland, T. tandanus of the Murray-Darling drainage and coastal streams of central-southern Queensland and New South Wales, and T. bostocki of southwestern Western Australia. The new species is distinguished from all congeners by a combination of the following morphologic characters: a high count of rays in the continuous caudodorsal and anal fins (range 153–169, mode 159), a high count of gill rakers on the first arch (range 35–39, mode 36), and strongly recurved posterior serrae of the pectoral-fin spine. Additionally, results from previously conducted genetic studies corroborate morphologic and taxonomic distinctness of the new species.