For decades policymakers have been attempting to negotiate multilateral climate agreements. One of the motivations for such agreements is the belief that securing cooperation among multiple states will induce greater political support for climate action. Voters may be more willing to adopt costly policies if other countries do so, both because the effort of other countries make it more likely that policies will be effective and because those efforts resonate with widely held reciprocity fairness norms. Yet, some recent research suggests that public approval of climate action is independent of the policy choices made by other countries. We present two different experimental studies fielded in multiple countries showing that multilateralism significantly increases public approval of costly climate action. Multilateralism makes climate policy more appealing by improving effectiveness beliefs and fair burden-sharing. Pursuing climate action within a multilateral setting does not only promise improved policy impacts, but may also generate higher levels of public support.