What explains populism? Recent research in political economy has demonstrated that economic factors have a striking impact on the support for populist parties. Among the economic factors that affect support for populism, inequality has received surprisingly little attention from scholars. More concretely, the existing literature has totally overlooked the extent to which beliefs in (in)equality can determine citizens’ sympathy towards these parties. I draw on the literatures on other-regarding preferences and economic voting, and argue that individuals care about equality, especially equality of opportunity, and that they will feel dissatisfied with their country’s political system whenever this is unable to provide equal chances to all citizens. I predict then that believing that there is no equality of opportunity will increase the identification with populist parties, whereas it will not increase that with social democrats. I use the 9th round of the European Social Survey to test my hypotheses. I find that my theoretical expectations are substantially valid: believing that there is inequality of opportunity increases the identification with populist parties (with both right-wing and left-wing populist parties) and decreases the identification with social democrats.