Do rebel group violations of international humanitarian law during civil war—in particular, attacks on noncombatant civilians—affect conflict outcomes? I argue that in the post-Cold War era, rebel groups that do not target civilians have used the framework of international humanitarian law to appeal for diplomatic support from Western governments and intergovernmental organizations. However, rebel group appeals for international diplomatic support are most likely to be effective when the rebel group can contrast its own restraint toward civilians with the government's abuses. Rebel groups that do not target civilians in the face of government abuses, therefore, are likely to be able to translate increased international diplomatic support into more favorable conflict outcomes. Using original cross-national data on rebel group violence against civilians in all civil wars from 1989 to 2010, I show that rebel groups that exercise restraint toward civilians in the face of government violence are more likely to secure favorable conflict outcomes. I also probe the causal mechanism linking rebel group behavior to conflict outcomes, showing that when a rebel group exercises restraint toward civilians and the government commits atrocities, Western governments and intergovernmental organizations are more likely to take coercive diplomatic action against the government. The evidence shows that rebel groups can translate this increased diplomatic support into favorable political outcomes.