Lord Sinclair is a title in the Peerage of Scotland. It was created in 1449 for William Sinclair, 3rd Earl of Orkney. In 1470, Lord Orkney surrendered the earldom in return for the earldom of Caithness. In 1477, Lord Caithness wished to disinherit his eldest son from his first marriage to Lady Elizabeth Douglas, William Sinclair (d. 1487), who was known as "The Waster". Therefore, so that his earldom would not pass to him, he resigned the title in favour of his son from his second marriage to Marjory Sutherland, who was also named William Sinclair (d. 1513) (who became the second Earl of Caithness). However, Lord Caithness was succeeded in the lordship of Sinclair by his eldest son William Sinclair, 2nd Lord Sinclair. The latter's son Henry, the third Lord, was confirmed in the title in 1488.
On the death of his great-great-great-grandson, the ninth Lord, the male line of the second Lord failed. He was succeeded by his grandson, the tenth Lord, the son of Catherine Sinclair, Mistress of Sinclair, daughter of the ninth Lord, and her husband John St Clair. In 1677 he obtained a new charter of the peerage confirming him in the title and with remainders respectively to his brother Henry Sinclair and his father's brothers Robert St Clair, George St Clair and Matthew St Clair, and failing them to his own heirs male whatsoever. However, his eldest son and heir John Sinclair, Master of Sinclair, was involved in the Jacobite rebellion of 1715 and attainted by Parliament. Consequently, he was not allowed to assume the title.
He died childless in 1750 when the claim to the title passed to his younger brother General James St Clair (d. 1762). However, he never assumed the title. On his death the lordship became dormant. It was to remain so until it was successfully claimed by Charles Sinclair, 13th Lord Sinclair, who was confirmed in the title by the House of Lords in 1782. He was the son of Andrew St Clair, de jure 12th Lord Sinclair, grandson of Charles Sinclair, de jure 11th Lord Sinclair (d. 1755) and great-grandson of the aforementioned Matthew St Clair, uncle of the tenth Lord. He thereby became the first holder of the title without descent from the original Lords. The thirteenth Lord, his son the fourteenth Lord, grandson the fifteenth Lord, great-grandson the sixteenth Lord, and great-great-grandson the seventeenth Lord, all sat in the House of Lords as Scottish Representative Peers. As of 2009 the title is held by the latter's only son, the eighteenth Lord, who succeeded on his father's death in 2004.
Lords Sinclair (1449)
- William Sinclair, 1st Earl of Caithness and 1st Lord Sinclair (d. 1480)
- William Sinclair, 2nd Lord Sinclair (d. 1487)
- Henry Sinclair, 3rd Lord Sinclair (d. 1513)
- William Sinclair, 4th Lord Sinclair (d. 1570)
- Henry Sinclair, 5th Lord Sinclair (1528–1601)
- Henry Sinclair, 6th Lord Sinclair (1581–1602)
- James Sinclair, 7th Lord Sinclair (d. 1607)
- Patrick Sinclair, 8th Lord Sinclair (d. 1615)
- Robert Sinclair b 04/04/1670<scotlandspeople.co.uk > Parish registers Haddington, East Lothian, Scotland
- John Sinclair, 9th Lord Sinclair (1610–1676)
- Henry St Clair, 10th Lord Sinclair (1660–1723)
- Charles St Clair, de jure 11th Lord Sinclair (d. 1775)
- Andrew St Clair, de jure 12th Lord Sinclair (1733–1775)
- Charles St Clair, 13th Lord Sinclair (1768–1863) (confirmed in title 1782)
- James St Clair, 14th Lord Sinclair (1803–1880)
- Charles William St Clair, 15th Lord Sinclair (1831–1922)
- Archibald James Murray St Clair, 16th Lord Sinclair (1875–1957)
- Charles Murray Kennedy St Clair, 17th Lord Sinclair (1914–2004)
- Matthew Murray Kennedy St Clair, 18th Lord Sinclair (b. 1968)