Whether United Nations peacekeeping operations are effective or not has been extensively studied over the past decades. Similarly, the differences between peacekeeping missions deployed by the UN and third party interventions by other actors are well documented. However, the interaction between blue helmets and parallel non-UN forces deployed alongside each other remains understudied. I aim to shed light on this phenomenon by answering the research question: Do Parallel Peace Operations moderate the effectiveness of UN Peacekeeping Operations? I argue that parallel non-UN operations reinforce UN peacekeeping missions in active conflicts by exercising active, kinetic measures of coercion. This increases the efficiency of the mechanisms of power applied by UN peacekeepers and makes it more likely that they fulfill the security related and socio-economic objectives of their mandate. A large-n analysis of all active conflicts between 1993 and 2014 suggests that as the UN commits more personnel to a peace operation, the security related objectives of its mandate are more likely to be fulfilled as long as the mission is supported by a parallel peace operation. I found more spurious and less convincing evidence for the moderating effect of parallel forces on the effective fulfillment of the socio-economic objectives of UN operation’s mandates.