Based on a case study of the Indian intervention in Sri Lanka's ethnic war from 1987 to 1990, this article explores the conditions under which democracies can act as effective third parties to resolve civil violence. India's experience as guarantor of a peace settlement in Sri Lanka suggests that not only the intractability of civil conflicts but the power of domestic pressures shape intervention policies and outcomes. Decision‐makers depend on the support of important domestic political elites ‐ political parties, interest groups, press, and governmental bureaucracies ‐ as well as the approval of the public who can reject them in periodic elections. In order to enforce peace settlements, third‐party guarantors must have a firm sense of the belligerents’ intentions and resources, sensitivity to the dynamics of the conflict, and freedom of action. At the same time, democratic leaders must consider the role of timing, the influence of internal bargaining, the importance of credible ‘staying power’, and personal reputation.