Grevillea raybrownii is a straggling shrub growing to 1.5 m (4 ft 11 in) tall. The leaves are linear and divide into 3-5 narrow lobes 2.5–5 cm (0.98–1.97 in) long on slightly intersecting branchlets that are smooth and rusty coloured when young. The lobes are spreading, sharply pointed, 0.5–2.4 cm (0.20–0.94 in) long and 0.6–1.2 mm (0.024–0.047 in) wide. The leaf upper surface is smooth and the underside has two grooves. The inflorescence is a dense cluster of about 40 flowers up to 2 cm (0.79 in) long, 1.5 cm (0.59 in) at the base, brownish coloured when in bud on a peduncle about 1 m (3 ft 3 in) long, at the end of branches or in the leaf axils. The perianth is white with a brownish limb, the inside is smooth and the outside covered in flattened dense silky hairs. The pistil is 6–7.5 mm (0.24–0.30 in) long and the style smooth. Flowering occurs in spring and the dry fruit is about 12 mm (0.47 in) long and densely covered in silky hairs.^[2][3]

Grevillea raybrownii was first formally described in 1994 by Peter Olde and Neil Marriott and the description was published in Telopea.^[4][5] The specific epithet (raybrownii) is in honour of Ray Brown, for his contribution to the horticulture of Grevillea.^[4]

This species has a restricted distribution, it grows in sandy, gravelly loams in dry sclerophyll forest, mostly on ridge tops, occasionally on slopes, between Dapto, Robertson and Berrima in New South Wales.^[5]

Grevillea raybrownii is listed as a "vulnerable species" under the New South Wales Government Biodiversity Conservation Act 2016.^[6]