The red fox (Vulpes vulpes) inhabits the most expansive global range of any wild carnivore. Since their introduction to Australia over 150 years ago, foxes have presented a significant threat to livestock and persistence of native species. Their success as an invasive species reflects their highly adaptable ecology, with few specific habitat requirements and an opportunistic, generalist diet. Bite force is often used as a predictive indicator of an animal’s feeding ecology. We analysed skull morphology (size, morphometry, weight) to estimate bite force for a large sample size of animals collected through culling. Over half (57%) of the 540 animals we sampled were juveniles (<1 yo; dispersing from their natal sites). Most variation in skull morphometry was driven by age: adults had significantly more robust skulls than juveniles, with greater estimated bite force. Sexual dimorphism (body mass and body length) was reflected in longer, heavier skulls of males. Sheep carrion comprised 47–65% of stomach contents volume; however, adult females ate less sheep but had more mice and invertebrates in their diet than males or juveniles of both sexes. This dietary separation for adult females is likely to reflect feeding behaviour and space use patterns rather than bite force limitations because juveniles (both sexes) showed as much consumption of sheep carrion as adult males, despite their lower estimated bite force than adults. This result highlights limitations of inferring diet partitioning from skull morphology alone.