This plant is usually unbranched, though branching forms are occasionally found. It is tall and distinctive, with large, lanceolate leaves (basal to 50 cm, cauline to 30 cm). The cauline leaves are long-decurrent. Flowers are in a tall spike, large (15–25 mm wide) and bright yellow. The upper three filaments are white or yellow-hairy, and the lower two filaments glabrous or only sparsely hairy.
Although not recorded in the county, some branching mulleins may in fact be a separate species, Showy Mullein (Verbascum speciosum). This has a candelabra-like appearance and several other subtle differences when compared to Woolly Mullein.