Brachylaena transvaalensis is an evergreen tree, although it can be deciduous at times depending on its location. It can grow to a height of between 10 and 25 metres. This tree produces a single straight trunk which at times is slightly fluted. Although the grey to pale brown bark is smooth initially, it becomes vertically striated and stringy with age. The grey twigs are ribbed and hairless.

The narrowly elliptic leaves are dark green and glossy above and white-felted below. They are alternate with a raised midrib underneath. The leaf margins are either entire or can be shallowly toothed towards the tip of the leavesand are often wavy.

The whitish flowers appear between July and September in dense clusters towards the tips of the branches. The flower stalks are either short or absent.

The fruit appear between September and November; the flower clusters produce clusters of small dry nutlets crowned with tufts of cream bristles.