Multi-stakeholder initiatives (MSIs) that address sustainability concerns have grown in importance in recent years. These private governance measures involving market, state and civil society actors aim to resolve disagreements between stakeholders through stakeholder engagement practices. However, our empirical study of the Mapuche conflict in Chile shows how a multi-stakeholder initiative contributed to the radicalization of a protest movement leading to an escalation of violence that left all actors worse off. The implementation of the Forest Stewardship Council (FSC) certification scheme, perhaps the best known MSI, exacerbated existing political discontent among the Indigenous Mapuche peoples who were resisting the expansion of industrial forest on their lands in southern Chile. Our findings indicate that MSIs cannot address the needs of marginalized stakeholders and may further undermine their interests. Our analysis enhances our understanding of the outcomes of MSIs by describing processes of radicalization as well as the role of the state in conflicts. The FSC certification scheme was incapable of addressing the key Mapuche demand for land rights. Instead, it raised false expectations, which coupled with corporate irresponsibility and state repression led to an escalation of violence. The increasing reliance on private governance measures in natural resource management, especially in countries of the so-called Global South, can further exacerbate existing conflicts and hence it is important to understand how and why MSIs lead to negative outcomes.