William Murray, 1st Earl of Mansfield, was the greatest judge in the history of the Anglo-American common law. Chief justice of the Court of King’s Bench for thirty-two years (1756-1788), Mansfield dominated the court with his extraordinary intellect and political acumen. Like the seventeenth-century philosopher John Locke, Mansfield believed that all law is based on reason and morality. His decisions in favor of religious freedom are particularly progressive and attractive to modern sensibilities. Influenced by Locke’s writings on toleration, Mansfield construed England’s harsh anti-Catholic laws so narrowly as to make them almost unenforceable. This angered many and may have led to the destruction of Mansfield’s London home and his papers by a mob in the 1780 Gordon Riots. This paper examines the sources of Mansfield’s views on religion and religious freedom and the relationship between these views and his overall judicial philosophy.