Archaeosynthemis leachii is a species of dragonfly of the family Synthemistidae, known as the twinspot tigertail. It is a medium-sized dragonfly with black and yellow markings. It inhabits streams, seepages and swamps in south-western Australia.
Archaeosynthemis leachii was originally named Synthemis leachii, and has also been known as Synthemis martini.