Conspiracy beliefs entail a scapegoating function by attributing the consequences of crises, such as economic downturns, to the secret action of outgroups. While conspiracy beliefs have been described as reactions to economic threats, we argue that this factor alone is not sufficient. Rather, perceiving one's ingroup as unfairly deprived compared to other groups (i.e., group relative deprivation) might be key to explaining the situation in terms of secret, intentional wrongdoings. Furthermore, individuals high in national narcissism (i.e., a perceived lack of recognition of the ingroup's greatness), may be especially sensitive to this dynamic. Three pilot studies (N = 1237) attested the robustness of the link between group relative deprivation and conspiracy beliefs. Then, Study 1 (N = 812) revealed that the effect of group relative deprivation on conspiracy beliefs was moderated by national narcissism. In Study 2 (N = 728), we found effects of induced national narcissism and group relative deprivation on conspiracy beliefs in a fictitious setting. Study 3 (N = 846) replicated the moderation of national narcissism on the link between group relative deprivation and conspiracy beliefs at the cross‐sectional level. Overall, these studies provide evidence that conspiracy beliefs in reaction to group relative deprivation are especially likely among collective narcissists. We discuss the scapegoating function of conspiracy beliefs during crises.