Today, republics—through the active participation of citizens in the political system—represent the dominant model of governance worldwide. Based on historical conditions, republicanism has emerged in two principal approaches: populism and nationalism, each with multiple components that, when examined within a political structure, can reveal the particular model of a republic. Following the Islamic Revolution, the Islamic Republic was established as the form of government, and the Constitution was drafted in 1979. Consequently, identifying its underlying approach is essential for understanding the structure of the state and for proposing strategies to enhance citizen participation in the political system. At the same time, the vocabulary employed in the Constitution may at times be ambiguous; therefore, referring to the framers’ views—as a conventional method of constitutional interpretation—can provide important clarification.The central research question of this study is as follows: “Based on the themes of the 1979 Constitutional Assembly debates, which approach—populism or nationalism—was adopted in designing the republican character of the Islamic Republic?” To address this question, the authors employed a documentary method for data collection and thematic analysis for data interpretation. The views of the members of the Assembly for the Final Review of the Constitution were analyzed with respect to Articles 1, 6, 8, 19, 20, 56, 59, and 100, in order to determine the role of populist and nationalist elements.The main contribution of the study—given the lack of prior research on this subject—is the demonstration that the republican structure of the Islamic Republic of Iran is populist at the socio-political level while being nationalist at the legal level.