Populism and beliefs in conspiracy theories fuel societal division as both rely on a Manichean us‐versus‐them, good‐versus‐evil narrative. However, whether both constructs have the same dispositional roots is essentially unknown. Across three studies conducted in two different countries and using diverse samples (total N = 1,888), we show that populism and conspiracy mentality have a strong common core as evidenced using bifactor modeling. This common core was uniquely linked to (aversive) personality, namely the Dark Factor of Personality (D), beyond basic personality traits from the HEXACO Model of Personality Structure. The association between D and the common core, in turn, was fully accounted for by distrust‐related beliefs as captured in cynicism, dangerous and competitive social worldviews, sensitivity to befallen injustice, and (low) trust propensity. Taken together, the results show that populism and conspiracy mentality have a shared psychological basis that is well described as a sociopolitically flavored manifestation of generalized dispositional distrust. The findings thus underscore the value of generalized trust for societal functioning and suggest that increasing trust may simultaneously combat both populism and beliefs in conspiracy theories.