These medium-sized monkeys are covered in thick golden fur with a green tint, which is how they get their common name, green monkeys. The face is hairless, but is covered with dark blue skin outlined by a soft line of white fur. Like other monkeys, they have long, slender, semi-prehensile tails. Males and females are sexually dimorphic. Males can weigh between 4 and 8 kg and measure an average of 500 mm in length. Adult females normally weigh between 3.5 and 5 kg and measure approximately 450 mm in length.

Males have blue scrotal regions and distinctly red penises. The combination of colours is said to present a distinctive “red, white and blue” display.

Green monkey locomotion varies little, regardless of habitat or substrate. In almost all circumstances, they travel quadrupedally on the ground or in tree canopies. Being relatively light, green monkeys are able to nimbly travel on the tops of branches using all four limbs.