A study of mitochondrial DNA showed it to be most closely related to the blue-bellied black snake (P. guttatus), with the Papuan black snake (P. papuanus) as the next closest relative to the pair.

[3] The most colourful member of the black snake genus Pseudechis, Collett's snake has dark brown to black upperparts, with pink or cream banding and sides, and pale yellow to orange underparts.

Juveniles are usually the same colour as adults but generally have brighter shades and contrast more.

Previously thought to be only moderately venomous to people, Collett's snake is now known to have been responsible for severe envenomation, with cases proceeding to rhabdomyolysis and acute kidney injury.

Early symptoms include nausea, vomiting, abdominal pain, diarrhea and headache, an anticoagulant coagulopathy, with risk of rhabdomyolysis and acute kidney injury within 24 hours if fluid replacement and black snake antivenom are not given.

The main diet of Collett's snake consists of amphibians, reptiles, and small mammals.