Indigenous Peoples’ lands cover over one‐quarter of Earth's surface, a significant proportion of which is still free from industrial‐level human impacts. As a result, Indigenous Peoples and their lands are crucial for the long‐term persistence of Earth's biodiversity and ecosystem services. Yet, information on species composition within Indigenous Peoples’ lands globally remains largely unknown. Here, we provide the first comprehensive analysis of terrestrial mammal composition across mapped Indigenous lands by using area of habitat data for 4,460 IUCN‐assessed mammal species. We estimated that 2,175 species (49%) have ≥ 10% of their ranges in Indigenous Peoples’ lands, and 646 species (14%) have > half of their ranges within these lands. For the threatened species assessed, 413 (41%) occur in Indigenous Peoples’ lands. We also found that 935 mammal species (of which 131 are threatened with extinction) have ≥ 10% of their range in Indigenous Peoples’ lands that have low human pressure. This analysis shows how important Indigenous Peoples and their lands are to the successful implementation of international conservation and sustainable development agendas.