Since the mid-nineteenth century, Iran and Afghanistan have shared a stable border delineated by the Anglo-Persian Treaty of Paris of 1857. Beyond the border, they share far more. First and foremost, they share the Persian language as the language of the state. Second, both Afghanistan and Iran were among the first “independent” Muslim-majority states of the twentieth century and shared parallel trajectories of political centralization and economic development under the reigns of Amir Amanullah Khan (1892-1960) in Afghanistan and Reza Shah Pahlavi (1878-1944) in Iran. Finally, they shared geopolitical concerns of sovereignty in the modern era and fear of Anglo-Russian competition for influence. This begs the question: what was the nature of the foreign relations between these two modernizing Muslim states that shared so much in common? Despite obvious commonalities, very little has been written on the diplomatic history of Afghanistan and Iran. The lack of focus is not unique to one of the historiographies, either—both Afghan and Iranian diplomatic and political historiographies are primarily dominated by the Great Game and relations with European states and focuses on one-man histories of Amanullah Khan and Reza Shah. The existing historiography thus excludes the role of bureaucrats in the development of Afghanistan’s political and diplomatic spheres and any significant engagement with diplomatic and political relations between Afghanistan and Iran. Sayyid Mahdī Farrukh (1886-1973), was Iran’s first vazir-i mukhtar to Afghanistan between 1926 and 1928. While in Kabul, he compiled troves of information in Kursīʹnishīnān-i Kābul, a diplomatic memoir with a didactic purpose. He also lead the signing of the ʿAhdnāma-yi vadādiya va taʿmīnī, (Agreement of Commitment and Security), a political and economic agreement between Afghanistan and Iran, the concerned with securing peaceful and prosperous relations that respected sovereignty. first of its kind between the modern states. Through a deep analysis of the primary sources, Kursīʹnishīnān-i Kābul and theʿAhdnāma-yi vadādiya va taʿmīnī, between Afghanistan and Iran, it is possible to understand the nature of the interest of Afghanistan and Iran in establishing formal diplomatic relations was based on their status as “independent” Muslim and Persian-speaking states and their desire to uphold political cooperation and maintain peace between the two bordering states.