Relevance. The development of cooperation between NATO (North Atlantic Treaty Organization) nations and their strategic partners, planned transition to the NATO standards of armed forces training require the priority of continuous professional development, and military leadership. It is no coincidence that the strategic goals of the Ukrainian defence reform include defence forces professionalization, armed forces manning with professionally trained, high moral standards of service members who are capable to solve comprehensive military professional tasks and lead military units in a changeable environment. The latter capability justifies the actuality of this topic to make military pedagogical theory more profound and renewal of academic practice of military specialists training considering modern realities and prospects of armed forces development.Purpose. The article is devoted to professionalization of experienced officer and characterization of military leader training.Methodology. The study employs a mixed-method approach, utilizing both theoretical analyses (review of literature and synthesis of concepts) and empirical methods (questionnaires and expert evaluations). This methodology provides a comprehensive view of the adult learning processes applicable to military leadership training.Results. Findings indicate that adult learning principles, particularly andragogy, significantly impact the professional development of officers. The research identifies key psychological and pedagogical conditions that foster effective military leadership, including the need for a supportive educational environment and the alignment of training methods with adult learning characteristics.Conclusions. The study concludes that integrating andragogy into military training programs significantly enhances the professionalization of officer-leaders. It advocates for educational strategies that are responsive to the adult learners' needs, emphasizing flexibility, self-directed learning, and practical application. Future research should further explore andragogical principles specific to military contexts to refine these training processes.