This dissertation seeks to illuminate early Stuart political history by a study of one important public figure. The fourth Earl of Dorset was a member of Charles I's Privy Council, Lord Chamberlain to Queen Henrietta Maria, and Lord Lieutenant of Sussex and Middlesex. He attended all the Parliaments of the 1620's, and sat in the Short and Long Parliaments. He was active in Court and Council throughout the 1630's, and sided with the King in the Civil War. He consistently advocated harmony and reconciliation in a period of growing polarisation. This study investigates Dorset's perception of early seventeenth century political developments, his response to them, and the reasons why he and other moderates failed to prevent civil war. It thus contributes to current debates both on the early modern peerage, and on the origins and nature of the English Civil War. The first chapter looks at Dorset's life and career up to the age of thirty. In Chapter Two a discussion of his rapid rise to political prominence during the 1620's explores the reasons for his success and the nature of his motivation. Chapter Three investigates Dorset's activities as a Privy Councillor and as the Queen's Lord Chamberlain in the 1630's. It analyses in turn the sources of his political power; his record as a patron; his relationships with other leading Caroline po1i ticians; his view of the Personal Rule; and his growing alienation from Charles I. Dorset's religious attitudes are reconstructed in Chapter Four, and the extent to which they determined his political behaviour is evaluated. Chapter Five assesses Dorse t 's strength as a local magnate, and discusses his landed estates, his career as Lord Lieutenant of Middlesex and Sussex, and his electoral influence. Chapter Six examines Dorset's attitudes to the breakdown of 1640-2 and to the Civil Wars. It shows how these motivated his involvement in peace negotiations, and considers why such negotiations failed. Dorset's sufferings at the hands of Parliament's finance committees are described in Chapter Seven, and the material cost of his Royalist allegiance is assessed. The Conclusion summarises the broader significance of Dorset's life and career.