This study draws upon Thomas Barton’s Forbes expedition journal, and a vast collection of manuscript letters, sermons, and other contemporary documents to illuminate his career and help readers appreciate the complex world of the pre-Revolutionary Pennsylvania frontier and more generally of the colonial American back country. As a missionary for the Church of England’s Society for the Propagation of the Gospel in Foreign Parts in York, Cumberland, and Lancaster counties of Pennsylvania, Barton championed the interests of the Anglican church and the proprietary of William Penn’s children in a turbulent borderland beset by both threats from the French and their Native American allies and challenges to English authority from a largely Scots-Irish Presbyterian population. After participating in General John Forbes’ successful campaign against the French stronghold of Fort Duquense during the French and Indian War in 1758, Barton assumed the incumbency of St. James church in Lancaster. In that city’s religiously turbulent and culturally diverse world, he advanced Enlightenment ideals and religious moderation. Targeted by extreme sectarian and political fanatics during the years leading up to the American colonies break with Great Britain, however, Loyalist Barton, ultimately deprived of his vocation and family, was evicted from Pennsylvania. After struggling against poor health and dire financial need in New York City for two years, he died in 1780, a self-defined martyr for his church and king.