It has a single narrow, pale green leaf and up to eight lilac-tinged blue flowers with the lobe on top of the anther covered with short, finger-like calli.

The side lobes have mop-like tufts of a few white to lilac hairs.

[2][3][4] Thelymitra cornicina was first formally described in 1871 by Heinrich Gustav Reichenbach and the description was published in Beitrage zur Systematischen Pflanzenkunde.

[5] The specific epithet (cornicina) means "horn-blower", hence "horn-shaped", referring to the column.

[3][6] The lilac sun orchid grows in scrubland and forest between Perth and Hopetoun in the Esperance Plains, Jarrah Forest, Swan Coastal Plain and Warren biogeographic regions.