This diurnal, arboreal species is largely associated with lowland tropical rainforest, preferring the lower levels; often in vegetation tangles; also be found in secondary habitat types and gallery forests (Gautier-Hion 2013). Common in mangroves along the coast of Congo (Maisels and Cruickshank 1996). Primarily a frugivorous species; also eats seeds, leaves, arthropods, fledgling birds and eggs (Tutin and White 1998). Density ranges from 4 to 66 individuals/km²; group size up to 22 individuals (Gautier-Hion 2013).

Cercopithecus cephus ranges from the Sanaga River in Cameroon south and east to the Congo River, to the lower Congo in the Democratic Republic of Congo (DRC). The northern limit appears to be the forest-savanna ecotone at about 5 to 6 degrees North. The area covered by the species distribution is about 836,650 km². The 2008 Red List assessment did not include the areas of the Mayombe in Gabon and Congo near the Gabon-Congo border, but they are still present in southern coastal Gabon (Aba’a et al. 2011, Mackaya 2011, R.J. Parnell pers. obs.) and Congo (MDDEFE 2010), and in southern Republic of Congo (Inkamba-Nkulu 2005). They were also in the Dimonika area in southern Congo to at least 1995 (Feer 1990, Ihobe 1995) and may still be there. 

Three subspecies are recognised: C. c. cephus occurs within about 70% of the species’ range, in Cameroon, Gabon, Equatorial Guinea, Congo and Central African Republic (CAR). It is limited to the north by the Sanaga River in Cameroon and the Ogooué River in the south. C. c. cephodes occurs south of the Ogooué River in Gabon, Congo, Angola (Cabinda) and a small area of coastal DRC, where its southern limit is the Congo River. A third subspecies C. c. ngottoensis is found in CAR, where it is known from the Kadei-Mambéré region east to the Ubangui, occurring as far north as Bangui and northern Congo; the southwestern limit is unknown.

This species is listed on Appendix II of CITES, Annex B of the EU Wildlife Trade Regulations and on Class B of the African Convention on the Conservation of Nature and Natural Resources.

This widespread species is present in all of the protected areas in Gabon, Equatorial Guinea, most PAs in Congo, in the forested PAs of southwest CAR, and in PAs south of the Sanaga in Cameroon up to, and including, the southern sector of the Mbam et Djerem National Park (Maisels et al. 2009). Occurs in one PA in Cabinda (Mayombe National Park; Ron 2011) and used to be - and may still be found - in the Luki Reserve in DRC (Pendje and Baya 1992). 

The recently described ngottoensis subspecies is present in the proposed Mbaere-Bodingue park in CAR, but absent from the Dzanga-Ndoki National Park and the contiguous Nouabalé-Ndoki National Park in Congo, and has not been recorded in any other protected area in that region (Brugière et al. 2005).