The Sinclair, later Sinclair-Lockhart Baronetcy, of Murkle in the County of Caithness and of Stevenson in the County of Haddington, is a title in the Baronetage of Nova Scotia. It was created on 18 June 1636 for John Sinclair, with remainder to his heirs male whatsoever. The third Baronet was a Baron of the Exchequer and member of the Privy Council of Scotland. The fourth Baronet married Martha, daughter and eventual heiress of Sir John Lockhart of Castlehill, a Lord of Session under the judicial title of Lord Castlehill. The eighth Baronet was an Admiral in the Royal Navy. On the death in 1899 of his son, the ninth Baronet, the title passed to a descendant of James Sinclair, younger son of the fifth Baronet, who in 1764 had inherited the Lockhart estates and assumed the surname of Lockhart. The tenth Baronet was a Major-General in the British Army and assumed the additional surname of Lockhart. The eleventh Baronet was the son of George Duncan Lockhart (whose grandfather had assumed the surname of Lockhart in lieu of his patronymic), another descendant of James, younger son of the fifth Baronet.