Known to locals as the lesula, the first specimen found was a young captive animal seen in 2007 in the town of Opala, scientists said.
Described in the open access journal PLoS ONE, Cercopithecus lomamiensis is only the second new species of African monkey discovered in the last 28 years, researchers said.
After the discovery of the captive animal, the study authors located additional lesula in the wild, determined the species genetic and anatomical distinctiveness and made initial observations of its behavior and ecology.
The new species' range covers about 6,500 square miles in central DRC, in one of Congo's last biologically unexplored forest blocks.
Although its range is remote and only lightly settled at present, the lesula is threatened by local bush meat hunting, the researchers said.
"The challenge for conservation now in Congo is to intervene before losses become definitive," said John and Terese Hart of the Lukuru Wildlife Research Foundation in Circleville, Ohio, who led the project.
"Species with small ranges like the lesula can move from vulnerable to seriously endangered over the course of just a few years."