Pelargonium vanderwaltii is a perennial, succulent to semi-succulent shrublet, up to 180 mm tall and 300 mm in diameter, much and irregularly branched, quite compact, winter-deciduous and slightly aromatic. The roots are fibrous. The ascending, rounded stems are 5–10 mm in diameter, green at first, becoming reddish brown, dark brown and smooth with age. The surfaces of young branches are covered with soft, white hairs (sericeous), becoming hairless (glabrescent) with age. The leaves are simple, crowded at the tips and ascending. The leaf blades are broadly egg-shaped to almost round 15–30(–50) × 25–38(–65) mm, the base heart-shaped (cordate). The margins are toothed (dentate), sinuate, and with a row of hairs (ciliate). The upper and lower surfaces are covered with soft hairs, the lower surface with prominent veins. The leaf tip is rounded. The petiole, 40–100 mm long, is persistent, drying to grey-white. The stipules are also persistent, triangular, 2 × 3 mm. The inflorescences are terminal, producing a 3-flowered pseudo-umbel, 50–70 mm in diameter; the peduncle short, 5–10 mm long, and the flower stalks 20 mm long. The sepals are linear-lanceolate, 5.0 × 1.5–2.5 mm, acute. The 5 petals are spoon-shaped (spathulate), rounded at the ends, varying from dark to pale mauve. The stamens, with 2 shorter, bearing white pollen. The seed (mericarps) is 5 mm long, the tail 12 mm long.