A political party is a modern political institution and refers to an organized group of individuals who share common political ideas and strive to achieve specific objectives. Among the most important functions of political parties are articulating and transmitting public demands to decision-making centers and enhancing the legitimacy and public acceptance of governing systems. Iran and Türkiye possess a long history of political parties and political organizations within the Islamic world. Nevertheless, both countries remain considerably distant from the optimal level of organization and effective public participation required for political development. It appears that, following the Islamic Revolution, the evolution of the party system in Iran has remained at the stage of expansion and has not yet reached the stage of institutionalization, whereas in Türkiye the party system has developed greater similarities with modern party models found elsewhere in the world. Given the cultural, social, and geographical proximity of the two countries, the present study comparatively examines the political systems of the Islamic Republic of Iran and Türkiye. Employing a descriptive-analytical method and drawing upon the theoretical framework of Patrice Duran, the study seeks to answer the following question: How has the nature of Iran’s Islamic religious political system, in comparison with Türkiye’s secular political system, influenced party policymaking in these two countries? The findings indicate that the religious political system of the Islamic Republic of Iran, compared with the secular political system of Türkiye, has exerted a direct influence on the party policymaking of both countries. The differences between their approaches to party policymaking are more substantial than their similarities. Finally, the respective strengths and weaknesses of each system are comparatively evaluated, enabling the study to offer recommendations for enhancing the performance and political role of parties in promoting genuine democracy, expanding public participation, strengthening popular legitimacy, and ensuring the sustainability of the governing system.