Eighty years ago Hunter Blair published his 'Memoir of John Patrick Third Marquess of Bute Kt.' Since then, all students of the subject have been dependent on this work, and there has been minimal research, with much of the Bute archive being inaccessible throughout these years. A new evaluation of the man and his achievements, making use of the huge quantity of relevant archival material now becoming available, was urgently needed. In addition to the Mount Stuart archive, much important material has been found in the archives of Sandon Hall, the NLS, BL and elsewhere. Using a biographical format, this thesis aims to go behind Hunter Blair's incomplete portrayal and uncover a more adequate picture of the man himself, his attitudes and his motivation, as well as his religious faith and philanthropy, his scholarly work and his artistic achievements. In particular, it looks for the unity of the person behind all these aspects, as revealed in his diaries and journals, and in the letters he sent and received. An extremely shy man, Bute presented a very different face to his closest intimates from the one which even Hunter Blair knew. His personal growth and development is traced from birth, shortly followed by his father's death, through an unusual upbringing and unorthodox education by his mother until his orphaning at the age of twelve. His adolescence was dominated by custodial battles, and was followed by years of religious conflict at Harrow and Oxford, culminating in his conversion to Roman Catholicism and his marriage. For reasons of space, the narrative concludes with the birth of his second child (first son) in 1881, when he was thirty three. Bute's achievements are set in the social context of mid-Victorian Britain, but the emphasis throughout is on their personal and interior dimensions. Questions addressed include the manner in which his extraordinary childhood affected his adult life, how his personal piety combined with sensuality to inspire his craftsmen to their fmest work, and how his aristocratic birth and great wealth, while at once burdensome and liberating in different ways, could often be set aside entirely. Despite his splendid buildings and fine historical writing, it is concluded that Bute's greatest accomplishments were personal, his gentleness with social inferiors, his positive attitude to women, and his forgiveness of those who had caused him most hurt.