Elachista velox is a moth of the Elachistidae family that is found in Australia, where it has been recorded from New South Wales, the Australian Capital Territory and Tasmania. The habitat ranges from mallee to rainforests. The larvae feed on Echinopogon species and various other grass species with soft leaves. They mine the leaves of their host plant. They mostly mine along the midrib of the leaf. The frass is deposited along the margin of the mine. Pupation takes place outside of the mine on the leaf of the host plant, under a loose web.