Barleria quadriloba is an unarmed shrublet, up to 400 mm high. The stems develop out of a woody rootstock and are covered with white hairs. The leaves are opposite, elliptic, dull green above and greyish green beneath, with long hairs on the veins and leaf margins. The leaf tapers into a petiole and the apex ends in a stiff point. The flowers are solitary in opposite axils (angle between the stem of the plant and the leaf stem), white with purple markings in the throat. The corolla (flower petals) is 2-lipped. The upper lip is 3-lobed and the bottom lip 1-lobed. Barleria lugardii and B. rehmannii are the only other barlerias in southern Africa that also have 4 petals, the rest of the species have 5 petals. The corolla tube is cylindrical and yellowish green. Each flower is subtended by modified leaves called the calyx lobes. The calyx lobes are ovate, with scattered white hairs on the lobe and lobe margins. The apex tapered into a stiff point. The bracteoles (secondary bracts) are leaf-like. Plants flower in late summer to winter (from January to June), during which time flowers appear sporadically.

The seed capsule is turgid at the base and ends in a long, conical beak. The ripe capsules burst open to distribute the seeds. There are 2 seeds per capsule.