What are the psychological roots of support for populist parties or outfits such as the Tea Party, the Dutch Freedom Party or Germany’s Die Linke? Populist parties have as common denominator that they employ an anti-establishment message, which they combine with some ‘host’ ideology. Building on the congruency model of political preference we expect that a voter’s personality should match with the message and position of her party. We theorize that a low score on the personality trait Agreeableness matches with the anti-establishment message and should predict voting for populist parties. We find evidence for this hypothesis in the United States, the Netherlands and Germany. The relationship between low Agreeableness and voting for populist parties is robust controlling for other personality traits, authoritarianism, socio-demographic characteristics and ideology. Thus, explanations of the success of populism should take personality traits into account.