The conservation performance of protected areas (PAs) is typically measured according to whether species are likely to be present within PAs. However, to attain the goal of long-term conservation it is important to consider the performance of PAs in terms of their ability to support the persistence of the species they contain. We used the concept of minimum viable population (MVP) size to examine the potential for PAs within a large national PA network to support mammal species over the long term. By developing habitat models for each species and estimating the area required to support the MVP size for each species, we identified whether each PA had sufficient habitat to meet the species’ requirements. We found that as a whole the PA network is able to support at least one viable population for all species studied. However, the extent of protection offered to species by the PA network varies considerably, with many PAs not able to support viable populations of individual species on their own. By understanding the capacity of PAs to provide long-term protection to species, our findings can guide strategies to increase the resilience of PA networks as a whole, including by improving habitat quality within and connectivity between PAs.