Collective narcissism - a belief in in-group greatness that is not appreciated by others - is associated with using one's group for personal benefits. Across one pilot and four studies, we demonstrated that collective narcissism predicts readiness to conspire against in-group members (rmeta-analysis  = .24). In Study 1, conducted in Poland (N = 361), collective narcissism measured in the context of national identity predicted readiness to engage in secret surveillance against one's own country's citizens. In Study 2 (N = 174; pre-registered), collective narcissism in UK workplace teams predicted intentions to engage in conspiracies against co-workers. In Study 3 (N = 471; pre-registered), US national narcissism predicted intentions to conspire against fellow citizens. Furthermore, conspiracy intentions accounted for the relationship between collective narcissism and beliefs in conspiracy theories about the in-group. Finally, in Study 4 (N = 1064; pre-registered), we corroborated the link between Polish national narcissism and conspiracy intentions against fellow citizens, further showing that these intentions were only directed towards group members that were perceived as moderately or strongly typical of the national in-group (but not when perceived in-group typicality was low). In-group identification was either negatively related (Studies 1 and 2) or unrelated (Studies 3 and 4) to conspiracy intentions (rmeta-analysis  = .04). We discuss implications for research on conspiracy theories and populism.