Baber Johansen was appointed Professor of Islamic Religious Studies at Harvard Divinity School in 2005. Prior to his appointment, he served as Directeur d'études at the Ecole des Hautes Etudes en Sciences Sociales (Centre d'étude des normes juridiques), Paris (1995-2005), and Professor for Islamic Studies at the Freie Universität Berlin (1972-1995). In 2006 he was appointed an affiliated professor at Harvard Law School and acting director of its Islamic Legal Studies Program for 2006 to 2010. In 2007, he was affiliated with the Department of Near Eastern Languages and Civilizations, and from July 2010 to June 2013, he was the director of the Center for Middle Eastern Studies. He is also a faculty associate of Harvard's Weatherhead Center for International Affairs and a member of its Executive Committee.
His research and teaching focus on the relationship between religion and law in the classical and the modern Muslim world. His book Muhammad Husain Haikal Europa und der Orient im Weltbild eines ägyptischen Liberalen (1967), translated into Arabic in Abu Dhabi in 2010, examines twentieth-century liberal interpretations of Islam; Islam und Staat (1982) looks at modern Muslim debates on state models; and Islamic Law on Land Tax and Rent (1988) considers long-term changes in classical and postclassical legal doctrine. Contingency in a Sacred Law: Legal and Ethical Norms in the Muslim Fiqh (1999) focuses on law, social practice, and ethics in Islam.
Johansen was twice elected a member of the School of Historical Studies, Institute for Advanced Study, Princeton, and has been a visiting professor at the Watson Institute (Providence), Harvard University, and Ca' Foscari (Venice). He is one of the three executive editors of Islamic Law and Society, and has served as area editor for Islamic Law in the Oxford Encyclopedia of Legal History (2009) and as adviser for the Encyclopedia of Law and Society (Sage, 2009).