This study analyzes the relationship between inter rebel group dynamics and rebel biased third party interventions. Concerning the considerable amount of multiparty civil conflicts and internationalized civil conflicts, prior studies largely overlook the cause and effect of inter rebel dynamics in terms of third party interventions. I delve into two related research questions; How do inter rebel dynamics influence a third party’s decision to intervene in a multiparty civil conflict? What kinds of rebel group interactions are facilitated by such third party interventions? Existing rebel group interaction patterns play a key role in determining conflict process and, influence third party’s decision to intervene. I predict that a cooperative interaction pattern between rebel groups generates an intervention enriched environment for the rebel groups, due to the increased likelihood of successful intervention and the decreased cost of war. The third party’s involvement in ongoing multiple party civil conflict generates a change in bargaining structure between rebels in terms of number of bargainers and distribution of capabilities. I predict a conditional effect of rebel biased interventions on inter rebel dynamics; while forceful intervention boosts cooperation between rebels, weak intervention fuels competition between them. To test my theoretical conjectures, the interlocking relationship between rebels’ interactions and rebel biased interventions has been empirically estimated on a large-N framework. The estimated results strongly confirm my theoretical predictions that rebel cooperation encourages rebel biased interventions and, that increased cooperation and competition is dependent upon third party’s commitment. Overall, my findings highlight a distinctive process of multiparty civil conflicts in terms of third party interventions and rebel group dynamics. My first findings regarding rebel biased interventions, expand the existing intervention literature by focusing on rebel group dynamics in multiparty civil conflicts. The empirical evidence showing boosted competition and cooperation caused by intervention, can be linked to studies that discuss the correlation between interventions and conflict terminations. For the policy community, this project suggests that the success of intervention lies in the third party’s measure of intervention.