The presented article completes the series of publications, which reflect the results of the development of theoretical-methodological foundations for socio-psychological research of the nation-building process from the standpoint of the subject-actional approach. It is made the theoretical analysis and synthesis of scientific ideas on the socio-psychological nature of the nation as a large social group, to determine the essence of a number of key conceptual constructs, namely: "nation-building as a collective activity", "people as a collective subject of nation-building", "functional structure of the nation-building process", "socio-psychological mechanisms of nation-building", etc. It is considered as one of the basic ones the contradiction between the scientific idea of spontaneous nature, the objective nature of the nation-building process, and the idea of the possibility of purposeful, organized creation of a nation by a certain community as a collective subject of social life. Thus, attention is drawn to the need to distinguish and reconcile the concepts of "nation-building" with its vague subjectivity, and "nation-building", which more clearly involves the actor, creator, subject. As a methodological basis of the study was chosen a subject-actional approach, adapted to the scientific knowledge of socio-psychological phenomena. Due to the above theoretical-methodological approaches, a hypothetical socio-psychological conceptual model of the nation-building process is developed. It consists of six structural-functional blocks, namely: block of the motivation of nation-building and corresponding goal-setting; instrumental block; block of decision-making on the transition from designing to the practical realization of nation-building goal; block of practical implementation of decision-making; block of nation-building results’ evaluation; block of creative generalization of nation-building experience as a basis for the transition to higher-level activities. It is established that working out of each structural-functional block presupposes achievement of a certain group psychological effect, in particular, concerning the first block – formation in participants of not simply thought or faith, but belief in truth and significance of nation-building idea, ability, and readiness by word and deed to defend these beliefs. Therefore, the key role in the organization of socio-psychological support of the nation-building activity of the collective subject here is given to the propositional mechanism of persuasion. Thus, the formation of a holistic conceptual idea of the structure, functions, mechanisms, and logic of the nation-building process as purposeful subject-action activity of its participants (people led by the spiritual elite) provided an opportunity to formulate a number of theoretical and methodological foundations of its socio-psychological research.