Leaders can be found at any hierarchical level of the organization, representing a determinant factor in the global performance and their subordinates’ level of job satisfaction. The present study aims to investigate the relationship between the leader’s attachment type and his leadership style, but also try to understand how this relationship can be impacted by the presence of accentuated personality traits. In this regard, data was collected using a set of self-report instruments (N = 110) from a sample consisting of 72 women (65.5%) and 38 men (34.5%) which take part in NGOs, between the ages of 19 and 43 years old. Results showed that the anxious attachment type significantly and negatively predicts efficient leadership styles, as opposed to the avoidant type that doesn’t seem to share such effects. Moreover, neither of the two insecure attachment types could significantly predict the leader’s inefficacy. Regarding to the effect that accentuated personality traits may exhibit, results indicated that Machiavellianism is the only dark trait which has a moderating effect on the relationship between attachment type and leadership style, but only at a lower level of the trait and in a way that reduces the efficacy of the avoidant leader. These results are characterized by a considerable practical importance, mainly in the fields of psychologists and social workers’ activity, in organizational selection and training.