Abstract Reducing Emissions from Deforestation and forest Degradation (REDD+) projects aim to contribute to climate change mitigation by protecting and enhancing carbon stocks in tropical forests, but there are no systematic global evaluations of their impact. Using a new data set for tropical humid forests, we used a standardised evaluation approach to quantify the performance of a representative sample of 40 voluntary REDD+ certified under the Verified Carbon Standard, located in nine countries. In the first five years of implementation, deforestation within project areas was reduced by 47954–68 compared with matched counterfactual pixels, while degradation rates were 58959–63. Reductions were small in absolute terms but greater in sites located in high deforestation settings, and did not appear to be substantially undermined by leakage activities in forested areas within 10-km of project boundaries. At COP26 the international community renewed its commitment to tackling tropical deforestation as a nature-based solution to climate change. Our results indicate that incentivising forest conservation through voluntary site-based projects can slow tropical deforestation; they also highlight the particular importance of targeting financing to areas at greater risk of deforestation. This article is protected by copyright. All rights reserved