GEORGE, 4th earl of Caithness (c. 1525-1582), a son of the 3rd earl, was a Roman Catholic and a supporter of Mary Queen of Scots, but he was mainly occupied with acts of violence in the north of Scotland. His grandson George, the 5th earl (c. 1566 1643), was outlawed and compelled to fly to the Shetlands. He left many debts, and his great-grandson and successor, George, the 6th earl (d. 1676), who was childless, arranged that his estates should pass to a creditor, Sir John Campbell, afterwards earl of Breadalbane. Campbell was created earl of Caithness in 1677, but the title was also claimed by George Sinclair (d. 1698), a grandson of the 5th earl, and in 1681 the privy council decided in his favour. When Alexander, the 9th earl, died in 1765 the title was suc cessfully claimed by William Sinclair (d. 1779), a descendant of the 4th earl, who became the loth earl.
The title of Lord Sinclair passed from William, the 2nd lord, who died about 1488, to John (1610-1676), who became the 9th lord in 1615. At first a covenanter, afterwards he became a roy alist, and was taken prisoner at the battle of Worcester. He died without male issue and the title became dormant. His estates, however, passed to his grandson, Henry St. Clair (1660-1723), the son of his daughter Catherine (d. 1666) and her husband, John St. Clair of Herdmanston, and in 1677 Henry was created Lord Sinclair with the precedence of the older title. He had two sons, John Sinclair (1683-175o) the Jacobite, and James Sinclair, who became a general in the British army, and was also ambassador at Vienna and Turin and a member of parliament for many years. After the attainder of John, in consequence of his share in
the rising of 1715, the family estates were settled on James, but he resigned them to his elder brother when the latter was pardoned in 1726. The pardon, however, did not include the restoration of the title. Earlier in life John Sinclair had killed a man named Shaw in a duel and had afterwards shot this man's brother. He was tried by court-martial and sentenced to death, but was pardoned. An account of the proceedings in the court-martial was edited by Sir Walter Scott for the Roxburghe Club (Edin burgh, 1828). Sinclair himself wrote Memoirs of the Rebellion, published by the Roxburghe Club in 1858.
Neither of the brothers left male issue, and the title devolved upon a cousin, Charles St. Clair (d. 1775), who was not included in the attainder. Charles did not claim it, but in 1782 his grandson Charles (1768-1863) was declared to be Lord Sinclair. He was a Scottish representative peer from 1807 to 1859 and is the ancestor of the present holder of the title.
See Sir R. Douglas, The Peerage of Scotland, new ed. by Sir J. B. Paul; G. E. (Cokayne), Complete Peerage; Sinclair, The Sinclairs of England (1887) ; Sir R. Gordon and G. Gordon, The Earldom of Suth erland (Edinburgh, 1813), and Hay, Genealogy of the Sinclairs of Roslin (1835).