Many countries write their constitutions with some form of international involvement. Internationalized constitutional assistance has been made easier by technology as well as trade and political exigencies. The question, therefore, is: How does this inevitable foreign influence impact constitutional legitimacy? This article discusses this question and asserts that foreign influence interacts with three approaches of constitutional design to shape constitutional legitimacy: (a) popular participation, (b) elites’ contracts, and (c) transnational constitutional implants. Such a transactional relationship is referred to as the “three-stone legitimacy theory”, which implicates both the internal and the external legitimacy of a constitution. The former means citizens’ acceptance that a constitution meets their aspirations, while the latter refers to the international community's satisfaction with the resulting constitution as guaranteeing the universal democratic ethos. The article ends with a proposition conceptualized as a “blueprint” for a democratic constitutional legitimacy in South Sudan.