This article explores how populist attitudes are correlated with foreign policy postures at the public level in four European countries: France, Germany, Great Britain, and Italy. We provide first evidence adjudicating between two rivalling perspectives. One perspective focuses on the ideational core of populism and argues that it entails substantive beliefs and values that may inform foreign policy preferences – just like any other ideology. Another perspective focuses on the thin-centredness of populism and argues that no policy implications can be derived from populist ideas. Analysing original survey data, we find strong and consistent associations of populist attitudes with two foreign policy postures, militant internationalism and isolationism, and weaker and less systematic associations with two others, cooperative internationalism and global justice orientations. Importantly, these patterns are independent of host ideologies. We discuss the implications of these findings for the question of how “thick” populism is and what that may mean for the politics of (European) foreign policies in times of a continuing populist Zeitgeist.