The European Union has gained salience as an issue in political debate. Recent literature shows that successful radical right-wing parties are frequently in opposition to European integration. This article looks at how radical left-wing parties’ positions on EU integration affect their electoral support. It argues that radical left parties can mobilize voters in their favour through positioning in opposition to EU integration because this allows voters to combine their left-wing economic and anti-EU preferences. Using expert and individual-level survey data, this research demonstrates that radical left-wing parties that position themselves against EU integration are more likely to gain individuals’ vote choice. This finding is surprising, given that traditionally radical left-wing parties are defined through their economic, rather than their non-economic, positions. This article demonstrates that variation in positioning around non-economic issues such as EU integration can explain differences in voter support across radical left-wing parties.