The northern quoll (Dasyurus hallucatus) is a carnivorous marsupial that has suffered severe population declines over the last 50 years and is now listed as Endangered. The Pilbara region of Western Australia is a semi-arid area that represents an extreme of the northern quoll's range. The overall objective of this study was to assess population characteristics of northern quolls at two rocky sites in the Pilbara, focusing on body condition, reproductive timing, population size, and sex-specific survival. We interpret these in the context of variation in habitat quality and the harsh climate. We found that reproduction occurred later in the year than in populations at more mesic locations where quolls have been previously studied, although their life history and demography were otherwise similar to that in other parts of their range. Contrary to our expectations, post-mating mortality of males was not complete. Population sizes differed between sites, suggesting that these rocky habitats varied in habitat quality. We suggest that local population size estimates can guide decisions on the relative importance of sites to ensure the long-term conservation of the species, given impacts of mining and the imminent invasion of introduced cane toads (Rhinella marina).