The south-eastern Australian helicarionid clade currently comprises six genera of snails and semislugs united by genital characters, including an epiphallic flagellum that produces a spiraling, spinose spermatophore, the absence of an epiphallic caecum, and the presence of at most a very short vagina. We comprehensively revise the taxonomy of this group based on comparative analyses of key morphological features and mitochondrial markers COI and 16S, revise the placement of several species described recently on the basis of shell morphology alone, and describe new taxa. The snail genus Brevisentis is monophyletic as currently understood, but includes an additional undescribed species from Wollemi National Park, New South Wales. Mysticarion is shown to contain four arboreal semislugs with wide, disjunct ranges, including one new species (Mysticarion obscurior sp. nov.). We synonymise Fastosarion staffordorum with Mysticarion hyalinus. The semislug Desidarion is synonymised with Parmavitrina, and we describe two new species of this genus, P. flavocarinata sp. nov. and P. maculosa sp. nov. The semi-arboreal semislug Cucullarion is herein included in the south-eastern Australian helicarionid clade based on morphological and genetic evidence, despite its more northerly distribution. Two small semislugs so far placed in Peloparion do not group together and a new genus, Ubiquitarion gen. nov., is described for Peloparion iridis. All of these genera, together with the semislug Helicarion (not included here), form a monophyletic radiation endemic to southeastern Australia.