Crabbea angustifolia is a prostrate, perennial herb, with trailing stems from a woody rootstock. The hairy stems are up to 400 mm long, with semi-erect to erect, narrowly lanceolate leaves. The leaves are hairy (especially on the underside), 70–130 × 7–12(–15) mm, with uneven or undulate margins, a narrow, acute tip and attenuate base.

The flowers are arranged in dense, compound, sessile, axillary heads (up to 40 mm in diameter) surrounded by bracts. The bracts are hairy and have long, straight or curved spines. The tubular to funnel-shaped flowers are white or cream-coloured and consist of 5 hairy, sub-equal, white petals; there are two yellow gibbous patches towards the throat of the corolla. The main flowering period is mid- to late summer (January–March).

Crabbea angustifolia is closely related to C. hirsuta, but is distinguished from the latter species mainly in having narrower leaves (7–12 mm vs 15–20 mm).