A new species and genus of acanthisittid wren (Aves: Passeriformes: Acanthisittidae) is described from the Early Miocene (1916 Ma) St Bathans Fauna from Otago, New Zealand, based on four fossil bones. The first Tertiary fossil passerine to be described from New Zealand, it is similar in size to New Zealand's smallest extant bird, the Rifleman Acanthisitta chloris. A phylogenetic analysis of 53 osteological characters and 24 terminal taxa, including four suboscines, basal corvoids (Menuridae, Atrichornithidae, Climacteridae, Ptilonorhynchidae, Maluridae, Dasyornithidae, Acanthizidae, Pardalotidae, Meliphagidae), and all seven Recent acanthisittid species, identifies it as the sister group to Acanthisitta. This, the first phylogenetic analysis of the basal passerine groups to use morphological characters, recovers a similar pattern of relationships of basal corvoid taxa to that obtained by recent molecular studies. The analysis also suggests that Acanthisitta chloris and the new species are the most deeply nested taxa within the family, suggesting that the radiation of Recent acanthisittids originated no later than the Early Miocene.