Callithrix penicillata can be found in Gallery Forest, dry forest and forest patches in the Cerrado of Central Brazil. As is true of other marmosets, they show a preference for disturbed and secondary growth forest (Fonseca and Lacher Jr. 1984; Lacher Jr. et al. 1984; Rylands 1984; Seabra et al. 1991; Rylands and Faria 1993).

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 behavioural 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; Rylands and Faria 1993). The most specialized of the Callithrix marmosets in this respect are Callithrix jacchus and C. penicillata (see Rylands 1984; Fonseca and Lacher Jr. 1984; Lacher Jr. et al. 1984; Rylands 1984; Rylands and Faria 1993). They live in extended family groups of between four and 15 individuals. Generally, only one female per group breeds during a particular breeding season. Associated with their tree-gouging and gum-feeding specialisation, groups generally have small home ranges: 1.25 ha to 4.5 ha (Fonseca and Lacher Jr. 1984); 3.5 ha (Faria 1986, 1989); 8.25 ha and 18.5 ha in IBGE Ecological Station (Brasília) (Miranda and Faria 1997); 2.5 ha and 6 ha in Universidade Católica de Goiás (Goiás) (Santana and Santee 1999);  6.0 ha in Universidade Católica Dom Bosco (Odalia-Rimoli and Rimoli 2007) and 50 ha in RPPN Fundação Universidade Federal de Mato Grosso do Sul (Ferreira et al. 2005, Santos, 2014), both in Campo Grande (Mato Grosso do Sul).

Callithrix penicillata has been the subject of a number of short studies (see, for example, Fonseca and Lacher Jr. 1984; Lacher Jr. et al. 1984; Faria 1984a,b, 1986, 1989; Miranda and Faria 2001; Vilela and Faria 2004; Vilela 2007).

Size:
Adult female: HB 209mm ± 9.0 (n=9) (Hershkovitz 1977); weight 307 g (n=8) (Smith and Jungers 1997).
Adult male: HB 209mm ± 9.0 (n=9) (Hershkovitz 1977); weight 344 g (n=8) (Smith and Jungers 1997).

C. penicillata has a very wide distribution, occurring mainly in the Cerrado region of east central Brazil, but can also be found in Atlantic Forest and Caatinga. According to Hershkovitz (1977) and Rylands and Mednes (2008), this species is endemic to Brazil and occurs in the states of Bahia, Minas Gerais, Goiás, Mato Grosso do Sul, the Federal District, the south-west tip of Piauí, Maranhão and the north of São Paulo, north of the Rios Tietê and Piracicaba, as a resident and native, and in the states of Espirito Santo, Rio de Janeiro, Paraná and Santa Catarina as a resident and introduced. In the north, it would seem that it is restricted to the south of the Rio Grande and Rio São Francisco (C. jacchus occurring to the north of the Rio Grande), although Vivo (1991) identified two skins in the Museu Nacional, Rio de Janeiro, from the north-east coast of Maranhão, at Miritiba (now called Humberto de Campos), which he indicated extends its range right through eastern Maranhão, along the left bank of the Rio Parnaiba. The large gap between the next northern most locality to the south (Canabrava, Rio Tocantins, Goiás, locality 275a of Hershkovitz 1977, p.490) and this northern Maranhão locality, indicates that they were probably introduced animals. They were not located by Hershkovitz (1977) and were presumed by him to be C. jacchus, following Ávila-Pires (1969). Silva Jr. (1999) carried out surveys in Maranhão and Piauí and did not report the occurrence of C. penicillata, only C. jacchus. The western limits of its range would seem to be marked by the Rio Araguaia, south from around 8ºS in the region of the Serra das Cordilheiras, extending into the north-east of the state of Mato Grosso do Sul, east of the Serra de Maracaju to the level of the Rios Pardo or Taquaraçú, west (right) bank tributaries of the Rio Paraná.

Surveys in the north of the state of Minas Gerais have shown that C. penicillata extends its range through the region between the upper Rio São Francisco and the Rio Jequitinhonha, along the western slopes of the Serra do Espinhaço. C. penicillata occurs both sides of the Rio Jequitinhonha as far east as the Rio Araçuaí, a south (right) bank tributary of the upper Jequitinhonha, beyond which it is restricted to the north of the river, with C. geoffroyi occurring to the south (Rylands et al. 1988), the result of a recent introduction (ca. 1975) in the vicinity of Belmonte (Coimbra-Filho unpubl. data). Callithrix penicillata is typically of the Cerrado region of Minas Gerais (in the central, south-west, west, and north of the state). Those parts originally covered by Atlantic Forest in the east and south-east (Zona da Mata) are the domain of C. geoffroyi, C. flaviceps, and in part of the Rio Doce valley, C. aurita. However, with the destruction of the forest and also introductions arising from misguided release of confiscated animals, C. penicillata is taking a hold and probably replacing other species in numerous localities east and south of its original range (see, for example, Olmos and Martuscelli 1995). This is happening in the Rio Doce State Park, and is possibly also the case of C. penicillata reported by Vivo (1991; see also Coimbra-Filho 1984) from the Itatiaia National Park straddling the border of the states of Rio de Janeiro and Minas Gerais. In both cases, C. aurita is the species naturally occurring in the area.
The current distribution of the taxon is probably reduced in relation to its historical range due to habitat loss, especially in the Cerrado. Its extent of occurrence is greater than 20,000 km² and its area of occupancy greater than 2,000 km².

C. penicillata has been introduced into protected areas in the state of Bahia, Minas Gerais, Rio de Janeiro, Santa Catarina and São Paulo. The following conservation units are within its geographical distribution (* indicates possibly introduced and/or mixed populations of C. jacchus and C. penicillata):

Chapada da Diamantina National Park (152,000 ha) BA (Rylands and Mendes 2008).
Raso da Catarina Ecological Reserve (104,842 ha)* BA (Rylands and Mendes 2008).
Brasília National Park (40,398 ha) DF (Coimbra-Filho 1984; Rylands and Mendes 2008)
APA Gama Cabeça-de-Veado (25,000 ha) DF (Miranda and Faria 1997, 2001;Vilela and Faria 2004),
Reserva Ecológica do IBGE (1,300 ha) DF (Lopes and Farias 2002).
Emas National Park (132,642 ha) GO (Coimbra-Filho 1984; Rylands and Mendes 2008).
Chapada dos Veadeiros National Park (65,514 ha) GO (Coimbra-Filho 1984; Rylands and Mendes 2008).
Acauã State Park (5,000 ha) MG (Rylands and Mendes 2008).
Caparaó National Park (31,762 ha) MG (Moraes and Melo 2007),
Fernão Dias State Park (2,000 ha) MG (Melo Júnior and Zara 2007)
Grande Sertão Veredas National Park (230,853 ha) MG/BA (Rylands and Mendes 2008).
Ibitipoca State Park (1,488 ha)* MG (Rylands and Mendes 2008)
Itacolomi State Park (7,543 ha)MG (Leão et al. 2007),
Pirapitinga Ecological Station (1,384 ha) MG (Rylands and Mendes 2008)
Rio Doce State Park (35,974 ha)* MG (Stallings and Robinson 1991; Instituto Estadual de Florestas 1994)
Serra da Canastra National Park (197,809 ha) MG (Coimbra-Filho 1984; Rylands and Mendes 2008)
Serra do Cipó National Park (31,639 ha) MG (Passamani 1996; Rylands and Mendes 2008)
Ilha Grande State Park (56,000 ha)* RJ (introduced)
Serra dos Órgãos National Park (20,024 ha)* RJ (Garcia 2005),
Taquara Natural Park (19,415 ha)* RJ (Burity et al. 2007),
União Biological State Reserve (2,922 ha)* RJ (Araujo et al. 2005; Pereira 2006, 2010),
Córrego  Grande Ecological Park (21.3 ha)* SC (Zago et al. 2007).
Ilha Anchieta State Park (828 ha)* SP (Melo Júnior and Zara 2007).
Araguaia National Park (?) (562,312 ha) TO (in range)

It is listed on Appendix II of CITES.