The article scientifically argues and develops conceptual and methodological principles of formation of legal competence of specialists in the system of life long education. It is confirmed that their training acquires efficiency when implemented according to specific theoretical and methodological research principles. The essence and content of the formation of legal competence of future specialists (on the example of accounting and taxation specialists), components (cognitive, motivational, activity, reflective and information-logical), criteria, indicators and levels of its formation are revealed. The pedagogical conditions of formation of legal competence of future specialists in accounting and taxation in the system of lifelong education are substantiated; theoretically developed and experimentally tested a comprehensive structural and functional model of the formation of their legal competence. It is proved that the application of the author's concept of formation of legal competence of specialists in the system of life long education, first of all, updating of content, the realization of defined and substantiated pedagogical conditions and developed structural-functional model, promotes the effective formation of all components of legal competence of future specialists. Checking the level of formation of the components of legal competence of future specialists in accounting and taxation in the system of lifelong education was carried out taking into account the defined structure of legal competence using the criteria defined in the study of its formation.