Bossiaea brownii is an erect shrub that typically grows to a height of up to and has hairy branchlets. The leaves are egg-shaped, mostly long and wide on a petiole long with narrow triangular stipules long at the base. The flowers are usually borne on short side branches, each flower on a pedicel long with a bract long and similarly-sized bracteoles at the base. The sepals are long and joined at the base with the upper lobes long and the lower lobes slightly shorter. The standard petal is yellow with a red base and about long, the wings purplish and long, and the keelpinkgrading to dark red and slightly longer than the standard petal. Flowering occurs in most months and the fruit is an oblong to ellipticpod long.