Recent scholarship has uncovered laïcité's Protestant sources by focusing attention on its late nineteenth- and early twentieth-century advocates. This article argues that the intellectual sources of laïcité stretch further back than this, namely to the writings of Jean-Jacques Rousseau (1712-1778) and Benjamin Constant (1767-1830). These two thinkers are rarely seen as allies. However, an examination of their views on religion reveals a surprising complicity, attributable in large part to their liberal Protestant sympathies. Benjamin Constant was well placed to understand and appreciate Rousseau's "Profession of Faith of the Savoyard Vicar" and his chapter "On Civil Religion" in the Social Contract. Moreover, Constant had observed firsthand the distortion of Rousseau's views by the French revolutionaries. This essay shows that Constant's writings on religion were those of a disciple of Rousseau, who wished to clarify and disseminate ideas that would prove foundational for the modern notion of laïcité.