We offer novel tests of hypotheses regarding the conditional relationship of psychological needs to political ideology. Using five personality measures and a large national sample, our findings affirm that political engagement plays an important moderating role in the relationship between needs for certainty and security and political identification, values, and policy preferences. We find that needs for certainty and security are strongly associated with right-wing political identification and cultural values and policy preferences, particularly among politically engaged citizens. In the economic domain, however, we find that needs for certainty and security are typically associated with left-wing values and policy preferences among politically unengaged citizens. It is only among politically engaged citizens that such needs are associated with right-wing economic values and policy preferences. Our findings confirm the importance of heterogeneity across both ideological domain and political engagement for how psychological needs translate into political ideology in the American mass public.