The ability to decipher drivers of densities for large carnivores will be critical in understanding their ecological requirements and develop conservation strategies. In this study, we used 164 camera trap stations, covering ~740 km2 over five distinct habitat types in the Udzungwa Mountains National Park and Kilombero Nature Reserve in Tanzania, to investigate drivers of density in one of the most widespread and adaptable large carnivores, the leopard (Panthera pardus). Data were modelled with an array of both biotic and abiotic covariates hypothesised to influence leopard density in a capture recapture framework. Results of stratified population models concluded that leopard densities declined with proximity to protected area borders and outranked prey availability, which was found to be the second most influential covariate explaining leopard density. We interpret these results of a negative effect on leopard population density as a direct effect of human activities, as Udzungwa is completely isolated and surrounded by agricultural development. Essentially this implies that protected area size limits leopard population size over prey abundance. Additionally, we found that leopard detectability was highest along water-ways and space-use was influenced the greatest by habitat type. Finally, the camera trap data found no exchange of individuals between habitat types despite being within the same protected area. Leopard density in the Udzungwa Mountains resembles that of exploited rainforest in West Africa and our study highlights the effects humans have on large carnivores deep into protected areas.