| Honorific Prefix: | Lieutenant colonel The Right Honourable |
| The Lord Sinclair | |
| Office: | Scottish Representative Peer |
| Term Start: | 9 June 1807 |
| Term End: | 23 April 1831 |
| Birth Name: | Charles St Clair |
| Parents: | Elizabeth Rutherfurd Andrew St Clair |
| Spouse: | |
| Relations: | John Rutherfurd (grandfather) |
Lt.-Col. Charles St Clair, 13th Lord Sinclair (30 July 1768 – 30 September 1863) was a Scottish noble and representative peer.
Charles Sinclair was born on 30 July 1768.[1] He was the eldest son of Elizabeth (Rutherfurd) St Clair (–1783) and Andrew St Clair of Herdmanston, de jure 12th Lord Sinclair.[2]
His paternal grandfather was Charles St Clair, de jure 11th Lord Sinclair (a son of Dr. Matthew St Clair, who was a younger brother of John Sinclair, 23rd Lord Herdmanston).[3] His maternal grandparents were John Rutherfurd, MP for Roxburghshire, and Eleanor (Elliot) Rutherfurd (a daughter of the Lord Justice Clerk Sir Gilbert Elliot, 2nd Baronet, of Minto). His uncle, John Rutherfurd, was also an MP for Roxburghshire, and married Mary Ann Leslie (a daughter of Maj.-Gen. Alexander Leslie and granddaughter of Alexander Leslie, 5th Earl of Leven).[4]
His claim to the Lordship of Sinclair was confirmed by the House of Lords on 25 April 1782.[5] He was an Ensign with the Royal Scots in 1784. He was made Lieutenant of the 17th Foot in 1788. He raised an independent company in 1790, which became part of the 15th Foot.[1] He became Captain in 1791, Major in 1795, and Lt.-Col. in 1799 before his retirement in 1802. He also served as a Lt.-Col. in the Berwickshire Militia from 1803 to 1805.[5]
Lord Sinclair in the House of Lords as a Tory Scottish representative peer from 1807 to 1859.[6]
Lord Sinclair was twice married. His first marriage was on 13 February 1802 to Mary Agnes Chisholm (d. 1814), the only daughter of James Chisholm of Chisholm. Before her death on 16 July 1814, they were the parents of:[7]
After the death of his first wife, he married Isabella Mary Chatto (d. 1875) on 18 September 1816. Isabella was the youngest daughter of Alexander Chatto of Mainhouse, Roxburgh. Together, they were the parents of:[7]
Lord Sinclair died on 30 September 1863 and was succeeded in the lordship by his eldest son James. His widow died on 5 June 1875.[8]