Research on the association of personality to political orientation has suggested that direct influences are modest. Here we used a personality system model in which direct influences on political behaviour flow from moral values, with personality mostly acting on these characteristic moral adaptations, rather than directly affecting political attitudes. Study 1 in 447 subjects supported this model, with significant effects on political orientation flowing from four of the five-factor model personality domains, but largely mediated through moral values concerning the importance of group order and individual rights. This personality system model was replicated in an independent study (n= 476) using a US sample and including a different measure of politics. Both studies support predictions that personality has significant effects on political attitudes, but that these are exerted largely via moral values. These findings help to explain inconsistencies in previous studies attempting to link personality to political orientation that have not included the intermediary level of values.