Polhillia stirtoniana grows upright, with a rounded shape, up to about 1 m in height. It often spreads wider than tall, forming a dense, bushy shrub. It has a woody rootstock and woody stems that form a dense, umbrella-like crown as it matures. Branches are greyish-brown, and the leaves are small, narrow, curved like a sickle, and covered with fine silvery hairs, giving the shrub a silvery appearance. Leaves stay tightly closed during dry weather and open slightly when it rains.

Flowers are bright yellow, small, around 9–11 mm long, with a greenish-yellow base covered with fine hairs and 1 or 2 flowers are produced per shoot. Pedicels are short, 1–2 mm long. Standard petal (the large upper petal) is hairy on the back surface. Calyx is up to 4 mm long, very hairy, and 2-lipped. It flowers in winter and spring (from June to September). Fruits are silky pods, pale olive-green, and do not split open when mature. Seeds are small, smooth, olive-green to dark brown, oval to kidney-shaped.