This study investigated the relation between the five-factor model (FFM) of personality trait domains and leadership effectiveness. Ninety-nine Australian Army commissioned officers completed the NEO Personality Inventory-Revised (NEO-PI-R; Costa & McCrae, 1992) and were rated by their superior officer on the Australian Army annual leadership effectiveness evaluation schedule. Participants indicated whether they had been selected to attend a leadership promotion course at the Army Command and Staff College, widely regarded within the Army as indicative of an officer's effectiveness. It was hypothesized that leadership effectiveness would be predicted by the personality trait domains of high Conscientiousness, Openness, Agreeableness, and Extraversion and by low Neuroticism. High Conscientiousness and low Extraversion scores predicted high leadership effectiveness and the likelihood of attending the leadership promotion course. High Openness scores also predicted the likelihood of attending the promotion course. The results support the utility of the FFM in exploring the role of personality in leadership effectiveness among military leaders.