Linking morphological studies with molecular phylogeny is important to understanding cryptic speciation and the evolution of host-parasite relationships. Haemosporidian parasites of the Australo-Papuan bird family Artamidae are relatively unstudied. Only one parasite species from the subfamily Cracticinae has been described, and this was based solely on morphological description. This is despite many Cracticinae species being easily observed and abundant over large ranges and in close proximity to human populations. We used morphological and molecular methods to describe a new Haemoproteus species (H. bukaka sp. nov.) from an endemic Butcherbird host (Cracticus louisiadensis) in a relatively unstudied insular area of high avian endemism (Papua New Guinea’s Louisiade Archipelago). Phylogenetic reconstructions using parasite cyt-b gene sequences placed the proposed Haemoproteus bukaka sp. nov. close to other host-specialist Haemoproteus species that infect meliphagid honeyeater hosts in the region, e.g. H. ptilotis. Distinct morphological characters of this haemosporidian include macrogametocytes with characteristic large vacuoles opposing a subterminal nucleus on the host cell envelope. Among 27 sampled individuals, prevalence of H. bukaka sp.nov. was high (74 % infection rate) but strongly variable across four islands in the archipelago (ranging from 0 to 100 % prevalence). Parasitaemia levels were low across all infected individuals (0.1–0.6 %). We suspect host density may play a role in maintaining high prevalence given the close proximity and similar physical environments across islands. The findings are discussed in the context of the host genus Cracticus and theory relating to parasite-host evolution and its conservation implications in Papua New Guinea.