Belief in conspiracy theories has been linked to various psychological factors, including threat perception, anxiety, and the need for control. However, little is known about the role of attachment orientations in shaping susceptibility to conspiracy beliefs. Drawing on attachment theory, the present research investigated whether adult attachment insecurity—particularly attachment anxiety—is associated with greater endorsement of conspiracy theories. Across two studies, we examined both correlational and experimental evidence for this relationship. In Study 1 (N = 192), attachment anxiety and attachment avoidance were assessed as dispositional predictors of generalized conspiracy belief, while controlling for well-established correlates, including right-wing authoritarianism, social dominance orientation, general anxiety, need for control, and relevant demographic variables. Results showed that attachment anxiety, but not attachment avoidance, significantly predicted conspiracy belief above and beyond these controls. In Study 2 (N = 149), we employed an experimental priming paradigm to test the causal effect of attachment anxiety on conspiracy belief. Participants exposed to attachment anxiety priming reported higher levels of belief in both generalized conspiracy theories and COVID-19-specific conspiracy theories compared to participants in a neutral priming condition. Together, these findings suggest that attachment anxiety constitutes a meaningful individual difference factor associated with susceptibility to conspiracy beliefs. The results support the notion that heightened threat sensitivity, difficulties in emotion regulation, and an increased need for control characteristic of attachment anxiety may predispose individuals toward conspiracy ideation, particularly in contexts marked by uncertainty and perceived threat. The present research extends existing models of conspiracy belief by integrating attachment-based processes and highlights the relevance of relational and affective factors in understanding why individuals differ in their endorsement of conspiracy theories.