Like many animals, DeBrazza's monkey existence is threatened by trade, destruction of habitat, fragmentation of their range, and cultivation. The males are much larger than the females. Males weigh around 7 kg and females around 4 kg. Males are closer to 60 cm in length and females closer to 40 cm. Both male and females have a long tail. This monkey takes shelter in trees. They shiver and freeze when scared by other animals. Debrazza monkeys gather food and fruits with their hands. They hunt in the early morning and early evening. The female gives birth to one baby. Daughters stay with mom their whole life. Sons leave when mature. While they live both on the ground and in trees, they do swim when necessary.

The Debrazza monkey is a "seed disperser" in the rainforest. Group sizes are exceptionally small, consisting of 4 to 10 monkeys, though groups have been found with up to 35 members. Unlike some other species of guenons, Debrazza's monkeys are rarely found associating with other monkeys. However, in captivity, they associate more freely. They are also excellent swimmers. Their predators are large African eagles, other primates, humans, and leopards. Communication between Debrazza's monkeys is both vocal and visual. Visual communication includes staring as a threat, sometimes with the mouth open but the lips covering the teeth. Another threat display is bobbing the head up and down. To reduce aggression in certain situations the lips are retracted showing clenched teeth. As an expression of tension or as another threat display, yawning by the adult males is performed to show the canines. Vocal communication consists of low boom calls to communicate territorially, and isolation calls often given by infant or juvenile monkeys when they become separated from the troop.