Abstract This article analyses the context of the first Brazilian antitrust law, between 1930 and 1945. Its goal is to clarify how the ‘popular economy’—a constitutional and legal concept of the time—functioned as a protective instrument for the internal market. The study explores the hypothesis that the legislation was directed at foreign economic power, already embedded in national economic structures at the time. The research demonstrates that the antitrust legislation arose not only to control prevailing economic power but also to provide meaning to it within the framework of the Estado Novo and its intent to reformulate the internal market. Furthermore, this article highlights the influence of constitutional and administrative doctrines in this movement, indicating how the antitrust system was modulated on liberal bases, assuming the curious figure of a strong State subsidiary to the private sector. The work demonstrates that, aside from the question of supply, a crisis in the insurance policy market throughout 1938 was crucial to drafting the first antitrust law.