A large number of factors have an impact on leadership effectiveness. One of the most commonly cited is the leadership potential of the leaders themselves. Leaders as individuals are defined in this manner by their inherited qualities and the personality-trait development they have either received or actually achieved themselves. Furthermore leadership (the conduct of leaders) is closely connected to leaders’ motivation, values and work ethic, and the power and authority that leaders acquire or build. To determine the extent to which leadership effectiveness is related to personality-trait based leadership potential, the paper presents a proposed model of effective leadership in the public sector, which covers the formation of personal leadership potential and identifying leadership effectiveness. The paper presents a trial application of the model in Slovenia, which offers a realistic representation of leadership potential and leadership effectiveness, which are at a relatively low level due to past neglect of this field in Slovenian central government units.