Delosperma purpureum is a captivating succulent perennial characterised by a somewhat woody taproot reaching up to 120 mm in length and approximately 15 mm in diameter. From the root apex arises a cluster of stems (hypocotyl), producing erect, fasciculate branches with basal vegetative growth. The stems attain heights of up to 90 mm and bear linear leaves measuring 10–40 mm in length, approximately 2.4 mm in width, and 2–4 mm in thickness. Leaf apices are straight and acute, while the upper surface is slightly channeled under natural conditions. Bladder cells are semi-globose, either smooth or with a small central dome.

Inflorescences are arranged in cymes and are borne above the foliage, often persisting in the following season as dried skeletal remains. Pedicels range from 8–20 mm in length. The flowers, measuring 10–23 mm in diameter, display deep purple petals arranged in one to two series, non-overlapping laterally, and lacking an inner series of shorter petals. Individual petals are 7–8 mm long and approximately 1.2 mm wide. The calyx lobes are unequal, measuring approximately 4.5 mm and 3 mm respectively. The flowers contain 16–22 filamentous staminodes and approximately 45 stamens. The fruit is a capsule, 4–5.5 mm in diameter, which senesces after one season. It detaches cleanly from its base before dispersal. The capsule apex is initially flat but later becomes centrally sunken, completing the reproductive cycle. Flowering occurs during the spring and summer months in South Africa.