A new species of chromodorid nudibranch, Goniobranchus solitaryensis sp. nov., is described from the Solitary Islands, northern New South Wales, Australia. The species is distinguished from all congeners by the combination of deep purple-black gills and rhinophores, a white mantle with scattered red spots including a characteristic pair of larger central spots that may coalesce into a transverse hourglass shape, and a broad golden-yellow mantle margin. Phylogenetic analysis of concatenated COI and 16S rRNA sequences places G. solitaryensis sp. nov. as the sister taxon to G. fidelis (Kelaart, 1858), from which it differs by a minimum uncorrected p-distance of 3.85% at COI (mean 5.42%). All other congeners are >14% divergent. The new species adds to the remarkable assemblage of red-spotted mimetic chromodorids in south-eastern Australia and is currently known from the Solitary Islands in the Mid-North Coast and Julian Rocks, in the Northern Rivers regions of New South Wales.