[3] Prasophyllum fuscum was first formally described in 1810 by Robert Brown from a specimen collected in "moist meadows towards George's River".

The description was published in Prodromus Florae Novae Hollandiae et Insulae Van Diemen.

[3] The slaty leek orchid is only known from a single population growing on a roadside in the Wilton district.

The total population of the species was estimated in 2007 to be twenty five individuals in an area of 4 km2 (2 sq mi).

The main threats to the population are habitat loss, changes to water quality and weed invasion.