In recent history, Indonesian forest policies have been dominated by deforestation in the name of economic progress. Many actors have expressed concerns about this trend and have tried to reverse it in favour of a more sustainable pathway. From 2004–2017, non-governmental environmental organisations fought for the case of the coastal Tripa peat swamp rainforest in the province of Aceh, Sumatra. Unique in Indonesian history, they managed halting and reversing the deforestation of an area. Their sustained action led the Indonesia state to cancel an oil palm plantation permit, with the plantation managers and owners facing heavy fines and prison terms. Our research seeks to understand the enabling factors making this success story possible. We used the Advocacy Coalition Framework for its capacity to deal with a complicated policymaking ecosystem whose decisions takes years for implementation. Our analysis found four enabling conditions of success, which were the NGOs capacity to: 1) sustain action for over a decade and grasp four changing events (post-tsunami reconstruction, emerging connection between forests and climate change, governors' change, and use of digital technologies); 2) learn from own past failures marked by the evolution of their policy core beliefs, from 'conserving forest for biodiversity' to 'conserving forest for local livelihoods', and then to 'conserving forest to prevent climate change'. As a result, they could broaden their advocacy coalition, which grew to include diverse social actors from local to international levels, including the central state's REDD+Task Force; 3) take an advantage over economic power by acting strategically and timely when changes occurred; and 4) closely monitor and disseminate knowledge (fire events, deforestation trends and peat depth), supporting a simple causal deforestation model which allowed a high degree of policyoriented learning, helping the coalition to change its behaviour and act strategically. To sum up, the overall trend of rainforest destruction for agricultural extension in Southeast Asia, particularly in Sumatra, Indonesia, can be reversed, at least at the local level. Cautious not to overgeneralise, the Tripa case indicates that NGOs could improve forest governance by engaging in the long term, acting strategically, and building a broad socio-ecological and rights-based coalition.