The Bullmastiff is a giant breed of dog, and there is evidence the breed is predisposed to cancer and musculoskeletal disorders, though the disease investigation of the breed is limited. This study reports on the demography, longevity and mortality of Bullmastiffs attending veterinary practices in Australia over a ten-year period. VetCompass Australia collects patient data from veterinary practices across Australia for epidemiological analysis. All patient records of Bullmastiffs available in the VetCompass Australia database during this decade period were reviewed, with demographic information on the breed inclusive of coat colour, sex, neuter status, weight and location collated. Standardised veterinary diagnostic (VeNom) codes for the most appropriate cause of death were assigned to deceased dogs. The population comprised 2771 Bullmastiffs with an overall median age of 2.8 years. Within the group, 1259 were female (45.4%), 1491 were male (53.8%), and 21 dogs (0.8%) had no recorded sex or neuter status. Dogs grew rapidly in their first year, with an average gain of approximately 1 kg every 10 days. A slower growth rate continued in their second year, and growth plateaued as adulthood was reached, with the mean body weight of adult male dogs (46.6 kg) being heavier than that of females (40.5 kg). The age at death for the group was 8.5 years. The most common causes of death in the breed were mass lesions (28.2%), old age (9.9%), musculoskeletal-related disease (9.9%) and neurological (5.3%) and behavioural disorders (4.8%). Neutering was protective against mortality from urogenital causes (OR: 0.14; CI: 0.02-0.52; = 0.003) and had a positive effect on longevity. This study provides demographic and health information on a population of Bullmastiffs attending veterinary practices in Australia, which will benefit evidence-based veterinary decisions for this breed. Additionally, the results may assist owners and breeders in making informed decisions on health risks and breeding programmes in the population.