In most Australian habitats, eucalyptus leaves are a significant part of the diet, but rarely the sole item eaten.

Around human habitations, common brushtails are inventive and determined foragers with a liking for fruit trees, vegetable gardens, and kitchen raids.

Its once vast distribution has been greatly affected by drought, epizootic disease and intrusion of invasive mammals into its habitat.

Its bushy tail (hence its name) is adapted to grasping branches, prehensile at the end with a hairless ventral patch.

[7][8] Its fore feet have sharp claws and the first toe of each hind foot is clawless, but has a strong grasp.

[7] The chest of both sexes has a scent gland that emits a reddish secretion which stains that fur around it.

In Australia, brushtail possums are threatened by humans, tiger quolls, dogs, foxes,[6] cats, goannas, carpet snakes, and powerful owls.

[17] The common brushtail possum can adapt to numerous kinds of vegetation but it is largely omnivorous.

The brushtail possum's rounded molars cannot cut Eucalyptus leaves as finely as more specialised feeders.

The brushtail possums' caecum lacks internal ridges and cannot separate coarse and fine particles as efficiently as some other arboreal marsupials.

They usually make their dens in natural places such as tree hollows and caves, but also use spaces in the roofs of houses.

[16] They vocalise with clicks, grunts, hisses, alarm chatters, guttural coughs, and screeching.

As usual for marsupials, the newborn may climb, unaided, through the female's fur and into the pouch and attach to a teat.

[7][8] Female young have a higher survival rate than their male counterparts due to establishing their home ranges closer to their mothers, while males travel farther in search of new nesting sites, encountering established territories from which they may be forcibly ejected.

In New Zealand's Ōrongorongo population, female young have been found to continue to associate with their mothers after weaning, and some inherit the prime den sites.

[25] The common brushtail possum is considered a pest in some areas, as it is known to cause damage to pine plantations, regenerative forest, flowers, fruit trees, and buildings.

Although once hunted extensively for its fur, the common brushtail possum is largely protected throughout Australia.

[31] Since its introduction from Australia by European settlers in the 1850s, the common brushtail possum has become a major threat to New Zealand native forests and birds.

The New Zealand Department of Conservation controls possum numbers in many areas via the aerial dropping of 1080-laced bait.