Forest conservation is essential for action on climate change and biodiversity loss. Forest loss and degradation are increasing around the world, including in the Amazon. It is widely reported that Indigenous communities can be effective in forest protection, but less attention has been paid to explaining how they are able to do this in the face of severe threats. This article investigates what can be learned from the success of the Kayapo Indigenous communities and their organizations in protecting more than nine million hectares of primary forest in one of the most highly degraded and deforested areas of the Brazilian Amazon. We use geographic information system analysis to demonstrate the extent of forest protection, along with field work to examine the crucial alliances with conservation NGOs from governance and planning perspectives. Our interdisciplinary analysis is guided by the three-pillar framework for integrated landscape management and is informed by interviews conducted with Indigenous and non-Indigenous staff working for the Kayapo NGOs. Based on this data and the experience of the Kayapo people, we identify the main factors that facilitated large-scale forest conservation. Our research also reveals that the work of the Kayapo NGOs aligns with the principles of strong governance and effective planning. Lastly, we discuss key lessons and critical considerations to ensure the continued viability and ongoing success of the Kayapo NGOs in achieving their objectives.