Leucaenaleucocephala is a shrub or small tree usually growing 2-10 m tall, but occasionally reaching 15 m or more in height.
The younger stems are green and usually densely covered in fine greyish coloured hairs (finely pubescent). Older stems have a relatively smooth, greyish or greyish-brown, bark with numerous small raised spots (lenticels). The leaves (up to 35 cm long) are twice-compound (bipinnate) and have 3-10 pairs of branchlets (pinnae). They are alternately arranged along the stems and borne on stalks (petioles) 2-5 cm long. A small raised structure (gland) is usually present on the leaf stalk (petiole), or just below where the lowest pair of branchlets (pinnae) meet. pinnae are 2-10 cm long and each bears 5-22 pairs of leaflets (pinnules).
These leaflets (7-21 mm long and 1.5-5 mm wide) are elongated (narrowly-oblong to lanceolate) in shape with pointed tips (acute apices), and are either hairless (glabrous) or have hairy (ciliate) margins. The fruit are elongated (linear), flattened, pods with a pointed tip (beaked apex). These pods (8-22.5 cm long and 10-20 mm wide) are initially green in colour, but turn brown or reddish-brown as they mature. Several pods will usually develop from each flower cluster. Each of these pods contains 10-25 hard seeds (6-10 mm long and 3-6 mm wide) that are glossy brown, flattened (compressed), and somewhat oval (elliptic-oblong) in shape.from February to April while fruiting takes place between July to October.