Mysticism, as a category long prominent in the study of religion, has been widely critiqued over the last quarter century for its essentialist illusions. That critical literature, while based on historicist convictions, has rarely extended such historical vision to the liberal religious culture that produced the modern construct. This article bridges the vast gap between Michel de Certeau's genealogy of “mysticism” focused on seventeenth‐century France and the accounts of those scholars who focus on the boom of academic studies at the turn of the twentieth century. It presents the emergence of “mysticism” as a category in Anglo‐American discourse from its development during the English Enlightenment within critiques of false religion to its Romantic remaking within Transcendentalist Unitarian circles in the United States. In taking seriously the religious and intellectual worlds that produced William James's theorizing, the article opens wider perspectives on why the construct came to carry so much weight in both the study and the practice of religion.