This mangabey is endemic to East Africa, and only occurs in two forests in the Udzungwa Mountains of south-central Tanzania. Although it is known from areas with altitudes of from , it is most common in mid-altitude evergreen forests, and mosaic woodland with mixed semi-deciduous and evergreen trees. It sometimes occurs in low altitude miombo woodland with Brachystegia species, and has been known to invade cropland. It frequents forested valley bottoms near watercourses, and also dry, more open slopes with scattered trees, bracken and Rubus species.