Protected areas are an important cornerstone in the attempt to halt habitat and species losses. While it is widely recognized that local communities impact on conservation outcomes, there is a limited understanding of the economic importance of environmental resources in protected areas to local household incomes and well-being. This inhibits the development and implementation of efficient conservation policies. This paper, using the iconic case of the Greater Serengeti-Mara Ecosystem and its surrounding local communities in Tanzania and Kenya, quantifies the household-level economic importance of this protected area. Data was collected using well-being and environmentally augmented structured household surveys administered to 985 randomly selected households in 25 communities. Results documented high reliance on environmental income of the poorest, a negative relationship between environmental reliance and well-being, with households closer to the protected area having higher environmental reliance and lower well-being. Hence, degradation of protected area habitats will negatively and disproportionately affect the income and may further reduce the well-being of the poorest households. Sustainable protected area management must address human well-being as well as conservation objectives. Increasing access to education and building skills to promote alternative non-environmental based livelihood activities will promote both conservation and development objectives.