While Muhammad Baqir al-Sadr has often been portrayed as a fundamentalist or sectarian Islamist, this study repositions the scholar as a revolutionary Shi'i modernist and a critical figure in global intellectual history. Drawing on a range of previously neglected primary sources, Rachel Kantz Feder explores how Sadr synthesized Islamic tradition with Marxist thought, Arab modernism, and global leftist critiques to articulate a distinct vision of religious, political, and cultural renewal. Set against the backdrop of mid-twentieth-century Iraq, the book situates Sadr within broader Arab and Islamic debates on modernity, nationalism, and state-building. It demonstrates how Sadr challenged both secular ideologies and clerical conservatism to promote popular sovereignty, social justice, and individual agency within an Islamic framework. Offering fresh insights into Islamic reform, Shi'i thought, and Cold War-era Arab intellectual history, this is an essential work for scholars and students of Islamic studies, Middle East history, political theology, and religious modernism.