This dissertation presents a biographical study of Philip Murray (1886-1952) who was one of America's premier labour leaders of the twentieth century. The work examines the major influences and historical events that shaped Murray's career. The thesis argues that Murray's career has been unfairly dismissed. It explains how the enduring effects of his formative years in Lanarkshire, Scotland, shaped his character as a trade unionist. It examines his early role as an official of the United Mineworkers of America (UMW A) in the 1920s and 1930s; his leadership of the Congress of Industrial Organizations (CIO) during the stormy era of its organising drive of America's industrial workers and of the Steelworkers Organizing Committee (SWOC); and his subsequent presidency of both the United Steelworkers of America (USWA) and the CIO during and after the Second World war. Murray's Catholicism and his relationship with Communists occupy a central position in the historical narrative. This thesis contends that Murray's motivations were not based on the crude antiCommunism of the McCat1hyism period following his death, and it seeks to prove the hypothesis that, in spite of his purging of the left-led unions inside the CIO, ironically, Murray throughout his life consistently strove to adhere to his class consciousness and uphold his convictions as a sincere advocate for labour's adversarial role inside capitalism. This thesis questions Murray's purported belief in class collaboration, as advocated in the papal encyclicals Rerum Novarum (1891) and Quadragessimo Anno (1931), and argues that, even if Murray agreed with the sentiments of the encyclicals' support and sympathy for the rights of workers and trade unions, he was never naive enough to reject the social and political reality of class struggle as an intrinsic, or motive, force in capitalist society.