This thesis comprises the only exhaustive examination to date of the life and career of Charles Boyle, 4th Earl of Orrery. Hailing from a family which dominated Anglo-Irish affairs throughout the 1600s, Orrery was an Irish peer of relatively modest means whose diverse career spanned not only politics and military affairs, but diplomacy, literary and scientific activities, and Jacobite conspiracies. His public career was facilitated in the 1690s by acclaim resulting from his role in the celebrated academic controversy between the Ancients and the Moderns. Court and family connections, associations acquired through scientific and literary interests, and his brother's untimely death enabled Orrery to win a Parliamentary seat and obtain an army commission, and, finally, to inherit the Orrery title and estates. Orrery's military and diplomatic activities were particularly noteworthy. Both were characterised by a sporadic, bitter rivalry with the Duke of Marlborough. Orrery's power and influence attained their greatest heights near the end of Queen Anne's reign and in the early years of the reign of George I. A client of John, 2nd Duke of Argyll for most of his life, Orrery remained closely linked to the Tory ministry of Oxford and Bolingbroke from 1710-1713 and played a crucial role in enabling that ministry to assume power. Later, due largely to personal dissatisfaction and misgivings about his future political prospects, Orrery reverted to a stance more palatable to the Hanoverian regime which was ushered in following Queen Anne's death in 1714. Orrery served briefly as Lord of the Bedchamber to George I, a position which afforded him intimate access to the sovereign and the court. Thereafter, however, Orrery's close ties to the previous administration apparently proved his undoing. By 1717 he had fallen from grace, lost all of his offices and perquisites, and defected to the parliamentary opposition. He then sought favour with the exiled Stuart Pretender, and later served as one of the principal Jacobite strategists in England during the 1720s. These activities led to charges of treason and a prolonged imprisonment in 1722-1723. Thereafter, Orrery lived out the rest of his life as a political outcast. He appears to have remained a devoted member of the opposition and a loyal Jacobite, although there is dubious evidence which suggests that he was in fact pensioned by the Hanoverians as a government informant. Orrery's rich career has been virtually ignored by scholars of the period. This thesis rectifies this neglect and in the process explores the world of early-eighteenth century diplomacy, court politics, intrigues, and intra-military rivalries.