The labellum has a glossy purple, mauve, or bronze-coloured beard with a ridge between the "eye" spots.

Calochilus robertsonii is a terrestrial, perennial, deciduous, herb with an underground tuber and a single fleshy, dark green, linear to lance-shaped leaf which is 150–400 mm (6–20 in) long and 8–12 mm (0.3–0.5 in) wide.

[3][4][5][6] Calochilus robertsonii was first formally described in 1873 by George Bentham and the description was published in Volume 6 of Flora Australiensis.

[1][7] The specific epithet (robertsonii) honours John George Robertson (1803–1862) who collected the type specimen.

[1][8] The purplish beard orchid is widespread and common in eastern Australia where it grows in a range of habitats from heath to forest and scrubland and from coast to mountains.