Sir William Sinclair, or Saint Clair (c. 1260—C. 1303), was the descendant of a line of Anglo-Norman barons, one of whom obtained the barony of Rosslyn from King David I. in the 12th century. Sir William took part in the dispute over the succession to the crown of Scotland in 1292, and was one of the leaders of the Scots in their revolt against Edward I. One of his sons was William Sinclair (d. 1337), bishop of Dunkeld, who was responsible for the defeat of an English force at Donibristle in Fife in 1317.

Sir William’s eldest son was Sir Henry Sinclair (d. I33o), the friend of Robert the Bruce; and Sir Henry’s son was Sir William Sinclair, who was slain by the Saracens in August 1330, while journeying through Spain to Palestine with Sir James Douglas, the bearer of the heart of Bruce. This Sir William Sinclair married Isabel, daughter of Malise, earl of Strathearn, Caithness and Orkney (d. C. 1350), and their son Sir Henry Sinclair (d. c. 1400) obtained the earldom of Orkney by a judgment of the Norwegian kingHaakon VI.in 1379. He then helped to conquer the Faeroe Islands, and took into his service the Venetian ftavellers, Niccolo and Antonio Zeno, sailing with Antonio to Greenland. This prince of Orkney, as he is sometimes called, was succeeded by his son Henry (d. 14I8), who was admiral of Scotland, and then by his grandson William (c. 1404—1480), the founder of the beautiful chapel at Rosslyn.

William, the 3rd earl of his line, whose earldom of Orkney was a Norwegian dignity, was made chancellor of Scotland in 1454 and Lord Sinclair and earl of Caithness in 1455. He tcok some part in public affairs in Scotland, and when in 1470 the Orkney Islands were ceded by Norway to King James III. he resigned all his rights therein to his sovereign and was known merely as earl of Caithness. His eldest son, William, having offended his father by his wasteful habits, the earl settled his earldom on his eldest son by another marriage, also called William, who was killed at Flodden in 1513. The elder William, however, inherited the title of Lord Sinclair, and the family was thus split into two main branches. John, the 3rd earl, was killed in 1529 while attempting to seize the Orkney Islands.

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 successfully claimed by William Sinclair (d. 1779), a descendant of the 4th earl, who became the 10th earl. James, the 12th earl (1766—1823), was descended from another branch of the 4th earl’s family, and his grandson James, the 14th earl (1821—1881), was a representative peer for Scotland from 1858 to 1868, and was created a peer of the United Kingdom as Baron Barrogill in 1866. He was interested in scientific matters, and published Lectures on Popular and Scientific Subjects (1877).

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 royalist, 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—1750) the Jacobite, and James Sinclair, who became a general in the British army, and was also ambassador ,to 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 Waiter Scott for the Roxburghe Club (Eclinburgh, 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.

Three brothers were also noted Sinclairs: Oliver, the friend of James V. and the leader of the Scots at the rout of Solway Moss; Henry (1508—1565), bishop of Ross and president of the court of session, who made some additions to Hector Boece’s Chronicles of Scotland; and John (d. 1566), bishop of Brechin.

Sir John Sinclair, Bart. (1754—1835), Scottish writer on finance and agriculture, was the eldest son. of George Sinclair of Ulbster, a member of the family of the earls of Caithness, and was born at Thurso Castle on the 10th of May 1754. After studying at Edinburgh, Glasgow and Trinity College, Oxford, he was admitted to the faculty of advocates in Scotland, and called to the English bar, but never practised. In 1780 he was returned to parliament for Caithness, and subsequently represented several English constituencies, his parliamentary career extending, with few interruptions, until 1811.

He established at Edinburgh a society for the improvement of British wool, and was mainly instrumental in the creation of the Board of Agriculture, of which he was the first president. His reputation as a financier and economist had been established by the publication, in 1784, of his History of the Public Revenue of the British Empire; in 1793 widespread ruin was prevented by the adoption of his plan for the issue of exchequer bills; and it was on his advice that, in 1797, Pitt issued the “loyalty loan” of eighteen millions for the prosecution of the war. His services to scientific agriculture were no less conspicuous. He supervised the compilation of the valuable Statistical Account of Scotland (2, vols., 1791—1799), and also that of the General Report of Scotland, issued by the Board of Agriculture; and from the reports compiled by this society he published in 1819 his Code of Agriculture. He was a member of most of the continental agricultural societies, a fellow of the Royal Societies of London and Edinburgh, as well as of the Antiquarian Society of London, and president of the Highland Society in London. Originally a thorough supporter of Pitt’s war policy, he later on joined the party of “armed neutrality.” In 1805 he was appointed by Pitt a commissioner for the construction of roads and bridges in the N. of Scotland, in I8io he was made a member of the privy council and, next year, received the lucrative sinecure office of commissioner of excise. He died on. the 21st of December 1835.

Sir John Sinclair, who was created a baronet in 1780, was twice married, first to a daughter of Alexander Maitland, by whom he had two daughters, and secondly to Diana, daughter of the first lord Macdonald, by whom he had thirteen children. His eldest son, Sir George Sinclair (1790-1868) was a writer and a member of parliament, representing Caithness at intervals from 1811 till 1841.

His son, Sir John George Tollemache Sinclair, the 3rd baronet, was member for the same constituency from 1869 to 1885. The first baronet’s third son, John (1797—1875), became archdeacon of Middlesex; the fifth son, William (1804—1878), was prebendary of Chichester and was the father of William Macdonald Sinclair (b. 1850), who in 1889 became archdeacon of London; the fourth daughter, Catherine (1800—1864), at one time enjoyed some vogue as an author.