Before neoliberalism became global, it was an intellectual project that had a particular view of the power of constitutions to limit sovereign states, anchor economic freedoms and protect markets from democratic pressures for greater equality. In Latin America and the developing world, neoliberalism has long been identified with the political economy of the Washington Consensus. However, the comprehensive study of its legal foundations and institutional arrangements is still an area of limited scholarly attention. This article attempts to advance in that direction. By examining the work of Friedrich A. Hayek, Milton Friedman and James M. Buchanan, it explores a theory of neoliberal constitutionalism within Chile, the so-called first neoliberal laboratory. These authors visited the country during the Pinochet dictatorship (1973–90), and were connected with top Chilean authorities as part of their global ambitions to implement their theoretical agendas in real-world scenarios. The article argues that Chile’s constitution-making process between 1973 and 1980 offered an on-site experiment in introducing neoliberal’s radical economic transformation. It addresses how the dictatorship’s natural law-based rule of law principles were compatible with the neoliberal constitutional ideology by supporting a distinctive view of the state’s role and designing the innovative institutional arrangements necessary to guarantee the market’s priority in the structural and rights dimension of the 1980 Constitution. In the wake of Chile’s recent constitutional change agenda, this article not only contributes to the existing debate by reflecting on the ideological origins of the still-persistent constitutional neoliberal features, but also works as a case study for evaluating new global turns towards authoritarian neoliberal politics.