There has been a great deal of discussion about the large volumes of foreign fighters involved in civil conflicts in Syria and Iraq over recent years. Yet, there remains little systematic evidence about the effect, if any, that foreign fighters have upon the conflicts they join. Existing literature distinguishes between the resources fighters bring to rebel groups and the liability they represent in regards to campaign cohesion. We seek to establish preliminary evidence as to whether or not foreign fighters contribute to the success of the campaigns they join. Our multinomial logistic and competing risks regression analyses of civil conflicts between 1946 and 2013 suggest that foreign fighters are associated with a decreased likelihood of government victory. Furthermore, we offer partial evidence to suggest that foreign fighters from non-contiguous countries are more likely to help rebels achieve a negotiated settlement or to continue their struggle against the government, but not to directly help them achieve victory.