UN blue helmets increasingly deploy in partnership with regional organizations and coalitions of states. While this development is hailed as a way out of geopolitical fragmentation and capacity overstretch, little is known about the effectiveness of these peacekeeping partnerships. We argue that UN and non-UN operations exercise different forms of power, which reinforce each other to reduce battle violence in active wars. If non-UN military operations actively engage in combat, the UN can focus on what it does best—employing its broad toolbox to coerce, induce, and persuade. Our quantitative analysis of the interaction between UN and non-UN peacekeeping supports these expectations: partnership peacekeeping works. With a non-UN partner, UN troops can reduce battlefield violence more effectively, that is, with fewer blue helmets. Importantly, non-UN missions need UN operations to successfully curb violence. The UN’s multidimensional engagement offsets the potential negative effects of an all-too militarized approach to violence reduction. Regional and coalition peacekeeping can only support the UN, not replace it.