Declines in global biodiversity due to land conversion and habitat loss are driving a "Sixth Mass Extinction" and many countries currently fall short of meeting even nominal land protection targets to mitigate this crisis. Here, we quantify the potential contribution of Indigenous lands to biodiversity conservation using case studies of Australia, Brazil and Canada. Indigenous lands in each country are slightly more species rich than existing protected areas and, in Brazil and Canada, support more threatened species than existing protected areas or random sites.