There is increasing evidence that right-wing populist parties (RWPPs) and their supporters are hostile to climate and low-carbon energy policies. In this article, we provide a quantitative analysis of the effects of RWPP representation in the legislature and executive on climate and renewable energy policy for a number of countries in the Organisation for Economic Co-operation and Development over the period 2007–2018. After controlling for other political, economic, and environmental factors, we find evidence for a significant and large negative effect of RWPPs in power on climate policy. Importantly, we also show that these negative effects vary with the proportionality of the electoral system and European Union membership. Both of these factors significantly moderate the negative influence of RWPPs. In countries with majoritarian electoral systems, the effects of RWPPs on climate policy work through both indirect legislative and direct executive routes. In contrast to climate policy, there is no overall significant relationship with renewable policy.