Thelymitra viridis is a tuberous, perennial herb with a single erect, pale green, fleshy, channelled, linear to lance-shaped leaf 100–250 mm (4–10 in) long and 5–12 mm (0.2–0.5 in) wide, sometimes with a purplish base.

The lobe on the top of the anther is usually yellowish, tube-shaped and gently curved with a small notch.

[2][3] Thelymitra viridis was first formally described in 2004 by Jeff Jeanes and the description was published in Muelleria from a specimen collected in the Rocky Cape National Park.

[4] The specific epithet (viridis) is a Latin word meaning "green",[5] referring to the overall pale greenish colour of this orchid.

[3] The green sun orchid grows in heath, near swamps and near rocks in coastal Tasmania.