Virtue was a concept of paramount importance in the American founders' republican thought. Without virtue, there could be no liberty, no order, no devotion to the common good, and no republican government. This dissertation examines the concept of virtue at the American founding, particularly virtue in the political thought of Mercy Otis Warren (1728-1814). The most important female intellectual of the Revolutionary generation, Warren wrote passionately about liberty and the beauty of republican ideals. Most important to this study, she consistently advocated the central place of virtue in a free and well-ordered republic. I argue that Warren incorporates three distinct philosophical threads - classical, bourgeois-marketplace, and Christian ideals - in her conception of virtue. I first analyze how Warren uses each of these three threads of virtue throughout her writings. I then examine how she synthesizes these individual threads into a single, cohesive conception of virtue. I argue that Warren consistently merges these ideals into a conception of virtue that she employs to address three pressing political problems of her day: How to motivate reluctant colonists to seek independence; how to check various forms of corruption spreading among the people; and how to counter corruption arising from commercial growth in the new nation. Modern political theorists often argue that these three threads, especially the classical republican and Christian ideals of virtue, are irreconcilable. My analysis shows that to divorce virtue from Christianity in Warren's conception is to rob it of its corrective vigor within republican government. I argue that what Machiavelli and Rousseau wrote out of republican virtue Warren writes back in. In Warren's political thought, virtue serves as the foundation for a stable enduring political system, provides the necessary informal ordering principle for the emerging republic, and offers the means by which the new nation could achieve its millennial destiny.