Across Europe, the use of negative portrayals of immigrants in populist political advertising has dramatically increased. An experimental study tested the underlying mechanisms and boundary conditions for the effects of such ads on explicit and implicit attitudes toward foreigners. Findings revealed that populist ads strengthened intergroup anxiety and negative stereotypes for voters with lower educational degrees. This, in turn, led to more negative explicit attitudes. However, we observed stronger effects of populist ads on implicit attitudes for individuals with higher educational degrees. The necessity of including explicit as well as implicit measures in political communication research is discussed.