This marmoset is an Atlantic forest species, occurring in lowland and sub-montane humid forest, in seasonal (mesophytic) rain forest, resting and white sand piaçava forest. Also known to use cabruca (cacao) plantations which are shaded with some native trees remaining from the original forest. They have been observed in secondary growth forest in abandoned rubber plantations. Callithix kuhlii is an adaptable species well able to live in degraded and secondary forests, depending on sufficient year round food sources and foraging sites. Near the coast, in the cocoa growing region, there is no distinct dry season with rainfall exceeding 2,000 mm per year (the heaviest rains are from March to June), but in the West of their range the forests are mesophytic with a distinct dry season. In some areas of its distribution the forests are semi deciduous, with rainfall as low as 1,000 mm per year (Rylands 1989, Pinto and Rylands 1997).

Marmosets and tamarins are distinguished from the other monkeys of the New World by their small size, modified claws rather than nails on all digits except the big toe, the presence of two as opposed to three molar teeth in either side of each jaw, and by the occurrence of twin births. They eat fruits, flowers, nectar, plant exudates (gums, saps, latex) and animal prey (including frogs, snails, lizards, spiders and insects). Marmosets have morphological and behavioral adaptations for gouging trees trunks, branches and vines of certain species to stimulate the flow of gum, which they eat, and in some species form a notable component of the diet (Coimbra-Filho 1972, Rylands 1984). They live in extended family groups of between four and 15 individuals. Rylands (1982) observed groups sizes of 5 to 9 individuals (mean 6.56 ± 1.33, n=8). Generally, only one female per group breeds during a particular breeding season. The groups defend home ranges of 10-40 ha, depending on the availability and distribution of food items and secondary-growth patches. Rylands (1982, 1989) recorded a home range size of 12 ha for a group of five individuals.

Rylands (1982, 1984, 1989) studied the behaviour and ecology of C. kuhlii at the Lemos Maia Experimental Station, Una, Bahia. Raboy and Dietz (2000) and Raboy et al. (2006) also studied this species in the Una Biological Reserve.

Endemic to Brazil, Callithrix kuhlii occurs between Rio de Contas and Rio Jequitinhonha in southern Bahia, just entering the north-easternmost tip of the state of Minas Gerais (Santos et al. 1987, Rylands et al. 1988, Neves 2008). The western boundary is still uncertain, but undoubtedly related to the inland limits of the Atlantic coastal forest. I.B. Santos (in Rylands et al. 1988) observed hybrids of C. penicillata and C. kuhlii in the region of Almenara, Minas Gerais, on the left bank of the Rio Jequitinhonha (16°41’S, 40°51’W). Neves (2008) surveyed the distribution of C. kuhlii and found individuals with hybrid phenotypes in 13 localities with dense tropical rain forest, at the western boundary of the species range, suggesting that the species is losing area to C. penicillata in this region (Neves 2008, Pereira 2015). Its range is largely coincident with that of the golden-headed lion tamarin Leontopithecus chrysomelas and these two callitrichids are broadly sympatric.
Surveys in 1986/1987 by Oliver and Santos (1991) demonstrated the presence of forms intermediate in appearance between C. kuhlii and C. penicillata north of the Rio de Contas, along the coast up to the regions of Valença and Nazaré, just south of the city of Salvador (Mittermeier et al. 1988). Individuals observed by Rylands near to Nazaré lacked the white frontal blaze, and, although retaining the pale cheek patches typical of kuhlii, were paler grey. A photograph of the marmoset from Valença, Bahia, north of the Rio de Contas, is shown in Mittermeier et al. (1988, p.19). The variation in pelage colour of the marmosets in this region is considerable, but Coimbra-Filho et al. (1991/1992) showed that true C. kuhlii extended north through coastal Bahia into the state of Sergipe as far as the Rio São Francisco. The present-day confusion has arisen from the widespread forest destruction, even more intense north of Salvador City, and the introduction and invasion of C. jacchus and C. penicillata.

Callithrix kuhlii occurs in some large strictly protected areas, including Una Biological Reserve (18,500 ha), Serra do Conduru State Park (8,941 ha), Serra das Lontras National Park (16,800 ha) and Una Wildlife Refuge (23,000 ha). The species is also present in some not officially protected areas, but well preserved and managed areas such as Lemos Maia Experimental Station (CEPLAC/CEPEC) (495 ha), Canavieiras Experimental Station (CEPLAC/CEPEC) (500 ha) and Djalma Bahia Experimental Station (CEPLAC/CEPEC) (145 ha). This species is listed in Appendix II of CITES.