It is a spreading to erect shrub with pinnatipartite leaves, the end lobes broadly triangular to oblong and sometimes sharply pointed, and dense clusters of greenish-white to fawn-coloured flowers with a white to cream-coloured style.

[2][3][4][5] Grevillea willisii first formally described in 1975 by Raymond Vaughan Smith and Donald McGillivray in the journal Muelleria, that was dedicated to commemorate the retirement of James Hamlyn Willis from the "National Herbarium, Melbourne" in 1972.

pachylostyla, from the upper reaches of the Buchan River, is similar to G. willisii, but was promoted to species status in 1994.

[7] Omeo grevillea grows on rocky granite outcrops near streams in the eastern highlands of Victoria, the shorter-leaved form near Omeo in the vicinity of the Mitta Mitta River and its tributaries, and the longer-leaved form near Nariel Creek and Wheelers Creek in the Corryong district.

[9] Grevillea 'Poorinda Royal Mantle' is a vigorous cultivar that was bred by Victorian plantsman Leo Hodge and registered in 1978; it is thought to be a hybrid between G. willisii and G laurifolia.