Galpinia transvaalica grows up to 6 m in height and is a multi-stemmed shrub or small tree. The stems are often crooked and the branches lie low. The bark is smooth and pale when young, but has a rough appearance and cracks into blocks when the tree is older.

The leaves are simple, opposite and have a glossy, dark to almost black appearance. They are 20-60 x 15-30 mm in size. The leaf apex is rounded and often notched; the margin is entire and noticeably wavy and the petioles are thick and thickset. Young leaves are coppery to reddish. The tree is very attractive in spring when the old leaves turn red before dropping and the coloured new leaves emerge. In late spring the tree may show a few red leaves hidden amongst the shiny new green foliage.

The flowers are white, up to 13 mm in diameter and borne in dense sprays at the end of branches. The bisexual floral parts occur in fives or sixes. The calyx is bell-shaped and divides into ovate lobes. The petals are crinkly, the ovary 2-chambered and the stamens are attached to the calyx tube. Flowers are present from November to May.

The fruit is a small, round capsule and 3-4 mm wide. It forms compact clusters that are reddish brown to black and is covered with a hard rind, which splits open to release winged seeds. Fruit appear from April to July.