* A personal, political and intellectual history of Irish communism and socialist republicanism between 1916 and 1962 * Murray left a significant imprint on Irish leftist politics through his work as an activist, prolific writer, propagandist and theorist * Uses newly-discovered archives relating to the Irish socialist and left republican movements, including letters from International Brigadiers during the Spanish Civil War This new biography explores the neglected life and political career of Sean Murray, who went from an unremarkable rural, northern Catholic upbringing to General Secretary of the Communist Party of Ireland and one of the most prominent left-wing thinkers of his era. An Irish War of Independence volunteer, anti-Treaty republican and graduate of the International Lenin School in Moscow, Murray rooted himself in the key Irish labour, republican and international struggles of his time. Using previously untapped sources, Sean Byers uncovers the details of Murray's IRA activities during the Irish revolutionary period, his significant contribution to the 1932 outdoor relief strike and the short-lived Republican Congress initiative, and his crucial role in organising the Irish contingent of the International Brigades in the Spanish Civil War. Shining a spotlight on Murray's close personal and political relationships with Peadar O'Donnell, Frank Ryan, Jim Larkin junior, Hanna Sheehy Skeffington, and many others, Byers reveals how cross-pollination between the Irish socialist and left republican movements was maintained by virtue of these relationships. This is a story of how in the face of adversity - the coercive measures of the Unionist state and red scare tactics of Catholic Ireland - Murray left a significant imprint on Irish leftist politics through his work as an activist and organiser, a prolific writer, propagandist and theorist.