This article focuses on the evolution of functionality of the Cabinet of His Imperial Majesty Peter the Great during his reign. Based on an analysis of materials from the collection of documents of the Cabinet stored in the Russian State Archive of Ancient Acts it indicates the scope of competence of the Cabinet Secretary A. V. Makarov (1674-1740) and the Cabinet of Peter the Great. The Cabinet of Peter the Great was engaged in financial support of administrative projects, building activities all-around Russia, military companies, diplomatic missions and many other things. In fact, it replaced and duplicated the functions of other institutions of central or local governments, more effectively solving the tasks since its head, Cabinet Secretary A. V. Makarov, had direct access to the monarch and had stable business ties with all state institutions without exception. The author also investigates how the role of this institution in the administrative system changed over time. The study shows the evolution from one clerk position, intended to be a personal royal secretariat, to an independent state institution with a broad scope of competence. The article concludes by arguing that the political significance of the Cabinet of Peter the Great directly depended on the place of A. V. Makarov in the system of public administration. Around the turn of the 1710s and 1720s, A. V. Makarov completely monopolized the intermediary function, through which the ruler was connected with other figures and institutions.