Breeding occurs from October to March, with up to two litters of 1-3 young per year. The young are weaned when about five weeks old. This common species occurs in a variety of habitats, ranging from wet and dry sclerophyll forests to buttongrass moorlands and coastal heath. It forms extensive systems of runways beneath dense vegetation. Grasses and sedges form the main component of the diet, although insects are occasionally taken.
Breeding begins in spring and runs to autumn.
More than one litter, of 3-5 young, may be raised per season. Females from the first litter of the season may give birth themselves during the same breeding season, as sexual maturity is reached at 3 months. Longevity is about 18 months. The brown rat is particularly common in urban areas, whereas the black rat also occurs in rural areas and adjacent bushland. In contrast to our native rodents, the black rat is known for the role it plays in the spread of disease.