This article proposes to explore the interaction between populism and environmentalism in the discourse of populist radical left parties, through a case study of Jean-Luc Melenchon's parties, Parti de gauche (2008-2016) and La France insoumise (from 2016). While an emerging literature primarily investigated the populist framing of populist radical right parties' climate (sceptic) discourse, the article analyses how a populist radical left party incorporates environmental issues into its agenda and the extent to which environmentalism and populism concretely interweave. Using mixed-methods, we first show that the logics of party competition and the growing salience of environmental issues led La France insoumise to gradually develop an ambitious green agenda. We then show that there is evidence for a populism/environmentalism nexus that could be defined as 'green populism'. La France insoumise's ecosocialist ideology combines to anti-elitism and people-centrism to blame the environmental crisis on the 'oligarchy' and to promote a green transition that would protect the people.