Campbell’s Monkey is found in a wide variety of habitats, including lowland forest, gallery forest, mangroves, woodland, woody savanna and farrow lands (Oates 2011, Campbell 2013). It also occurs in secondary forest, in areas of subsistence agriculture, and in farmbush. The highest elevation area where this species occurs is the lower latitudinal locations (up to 600 m) in the Guinea Highlands. The estimated home range size for two groups in Taï NP was 52 ha and 67 ha (Buzzard and Eckardt 2007). C. campbelli mainly feeds on fruits and insects. In Taï NP, the diet of this species was found to be 46% fruits, 33% animal matter and 8% leaves (Buzzard 2006). Foraging for insects often involved unrolling curled-up leaves.

The typical group structure is a one-male group, but the species is sometimes found in multi-male groups, and all-male groups outside heterosexual groups have been observed (Galat and Galat-Luong 1985, Buzzard 2006). In Taï NP in 1976, mean group size was 11.4 individuals (5–33, N=8) (Galat and Galat-Luong 1985), but had decreased to 9.3 (N=3) in 2001 (Buzzard and Eckardt 2007). Group size in Guinea-Bissau ranged from 1–20 (Gippoliti and Dell'Omo 2003). On Tiwai Island, mean group size recorded in 1982–1984 was 14 (Oates et al. 1990).

This species is preyed upon by Leopards (Panthera pardus), Western Chimpanzees (Pan troglodytes verus), and Crowned Hawk-eagles (Stephanoaetus coronatus) (Zuberbühler and Jenny 2002).

Campbell’s Monkey ranges from the Gambia and Senegal, just north of the Casamance River in the west, through Guinea-Bissau, Guinea, Sierra Leone and Liberia to the Cavally River on the Côte d’Ivoire-Liberia border in the east (Oates 2011). Between the Cavally and Sassandra-Nzo Rivers in western Côte d’Ivoire is a region where individuals of this species and of Cercopithecus lowei occur, as well as individuals with intermediate features (Oates 1988, 2011). This species also occurs on the island of Caravela in the Bijagos Archipelago of Guinea-Bissau (Gippoliti and Dell'Omo 2003).

Cercopithecus campbelli is listed on Appendix II of CITES and Class B of the African Convention on the Conservation of Nature and Natural Resources.

This species occurs in many protected areas in its geographic range (e.g., Gola Forest NP, Loma Mountains NP, and Tiwai Island in Sierra Leone; Sapo NP and Grebo NP in Liberia; Taï NP in Côte d'Ivoire), but anti-poaching enforcement is poor in Sapo NP and in the northern sections of Taï NP away from the research station. Rigorous law enforcement against poaching and in protected areas is needed throughout the range. Protection is sometimes improved where there is a permanent presence of researchers (e.g. southern Taï NP).