This study explores how Alexander the Great’s conquest of Iran introduced Greek political ideas, particularly those of Aristotle, leading to a shift from traditional Persian kingship toward participatory governance inspired by Athenian city-states. During the Parthian era (247 BCE–224 CE), this ideological break raises the question of whether Iran’s ancient history contains early roots of constitutional monarchy. The research argues that the Parthians, by diverging from the classical "Iranian kingship" model and adopting Hellenistic political concepts, established institutions like the Assembly of Elders (Megistanes) and local councils. These structures fostered a dynamic civil society, creating a proto-constitutional system where the king’s power was checked by aristocratic and democratic mechanisms. The study examines historical evidence to demonstrate that the Parthian monarchy was not absolute but functioned within a framework of shared governance, blending Persian traditions with Greek political thought. The hypothesis posits that the Parthian system—marked by consultative bodies, decentralized authority, and civic participation—laid the groundwork for later constitutional developments in Iran. By analyzing primary sources and comparative models, the paper challenges the notion that constitutionalism in Iran emerged only in modern times, instead tracing its origins to ancient hybrid governance under the Parthians.