Head and body length of O. crassicaudatus is 270-465 mm, tail length is 325-520 mm, and weights range between 600-2,000 grams. The fur is pale gray tinged with buff or brown, generally darker around the eyes and the underparts and bushy tail are lighter. As in Galago, the ears are ridged, allowing the animal to furl and unfurl them independently from each other.

Greater galagos prefer forests, thickets and well-developed woodlands, but may occur in urban areas where there is a sufficient amount of shelter and food. O. crassicaudatus is nocturnal, using a nest for sleeping during the day. The main diet consists of tree gums, supplemented by insects. Social groups contain between two and six individuals which include an adult pair with or without young, or one or two adult females with young. All of the individuals in the group sleep together during the day, but the adults will separate at night when foraging. Vocalization is a loud croaking wail, which appears to coincide with the breeding season, but is also used to announce the animal's presence. Urine washing of fore and hind limbs is also used to disseminate the galago's scent.

Estrous cycles last about 44 days and gestation is about 133 days producing usually two, and sometimes 3, offspring. The babies, who weigh about 40 grams at birth, are born with their eyes open. They are able to feed on their own at 1 month, but may continue to nurse until about 5 months old.

O. crassicaudatus is found in Kenya, Tanzania and Rwanda to KwaZulu-Natal (South Africa) and Angola.