The boomslang is thought to be closely related to members of the genera Thelotornis, Thrasops, Rhamnophis, and Xyelodontophis, with which it forms the taxonomic tribe Dispholidini.

Males are light green with black or blue scale edges, but adult females may be brown demonstrating sexual dimorphism.

The maxillary teeth are small anteriorly, seven or eight in number, followed by three very large, grooved fangs situated below each eye.

The dorsal scales, which are arranged in 19 or 21 rows, are very narrow, oblique, strongly keeled, with apical pits.

[10] The boomslang is oviparous, and an adult female can produce up to 30 eggs, which are deposited in a hollow tree trunk or rotting log.

[11] During cool weather, the boomslang brumates for short periods, often curling up inside the enclosed nest of a weaverbird.

[12] The venom of the boomslang is primarily a hemotoxin; it works via a process in which many small clots form in the blood, causing the victim's circulatory system to improperly coagulate, resulting in excessive bleeding and death.

The venom has been observed to cause bleeding in tissues such as muscle and the brain (among other organs), while, at the same time, clogging capillaries with tiny blood clots.

[2][13] Other signs and symptoms include headache, nausea, sleepiness, and confusion, leading to cardiac arrest and unconsciousness.

[18] In 1957, herpetologist Karl Schmidt died after being bitten by a juvenile boomslang, which he had doubted could produce a fatal dose.

The boomslang is a timid snake, and bites generally occur only when people attempt to handle, catch, pursue or kill the animal.

When confronted and cornered, it inflates its neck and assumes an S-shaped striking pose, a key indicator of any snake species feeling threatened.