It is a prostrate to low-lying or straggling shrub with deeply divided leaves, the end lobes triangular, and toothbrush-shaped clusters of reddish-brown flowers with a red style.

The end lobes or teeth are usually sharply pointed and the edges of the leaves curve downwards.

Flowering occurs from November to December and the fruit is a silky-hairy follicle 9.5–11.5 mm (0.37–0.45 in) long.

[2][3][4] Grevillea microstegia was first formally described in 1975 by Bill Molyneux in the journal Muelleria from specimens collected in 1970 on Mount Cassell in the central eastern ranges of the Grampians National Park.

[4] Mount Cassell grevillea grows on sandy or rocky soil in forest and scrub in the William Range area of the Grampians National Park.