| Honorific-Prefix: | The Right Honourable |
| The Earl of Rosslyn | |
| Honorific-Suffix: | PC DL |
| Order1: | Master of the Buckhounds |
| Term Start1: | 10 September 1841 |
| Term End1: | 29 June 1846 |
| Monarch1: | Victoria |
| Primeminister1: | Sir Robert Peel |
| Predecessor1: | The Lord Kinnaird |
| Successor1: | The Earl Granville |
| Term Start2: | 28 February 1852 |
| Term End2: | 17 December 1852 |
| Monarch2: | Victoria |
| Primeminister2: | The Earl of Derby |
| Predecessor2: | The Earl of Bessborough |
| Successor2: | The Earl of Bessborough |
| Term Start3: | 18 January 1837 |
| Term End3: | 16 June 1866 Hereditary Peerage |
| Predecessor3: | The 2nd Earl of Rosslyn |
| Successor3: | The 4th Earl of Rosslyn |
| Birth Date: | 15 February 1802 |
| Nationality: | British |
| Party: | Tory |
| Parents: | James St Clair-Erskine, 2nd Earl of Rosslyn Harriet Elizabeth Bouverie |
| Children: | 3, including Robert |
General James Alexander St Clair-Erskine, 3rd Earl of Rosslyn PC, DL (15 February 1802 – 16 June 1866), styled Lord Loughborough from 1805 to 1837, was a Scottish soldier and Tory politician. A General in the British Army, he also held political office as Master of the Buckhounds between 1841 and 1846 and again in 1852 and as Under-Secretary of State for War in 1859.
Rosslyn was the son of James St Clair-Erskine, 2nd Earl of Rosslyn, by his wife Harriet Elizabeth Bouverie, daughter of the Hon. Edward Bouverie (the second son of Jacob Bouverie, 1st Viscount Folkestone).
Rosslyn entered the British Army in 1819. He purchased a captaincy in the 9th Light Dragoons in 1823 and a lieutenant-colonelcy in 1828. He was promoted to Major-General in 1854, to Lieutenant-General in 1859 and to full General on 20 April 1866.
In 1864 he was appointed Regimental Colonel of the 7th Queen's Own Hussars after the death of General Sir William Tuyll. Lord Rosslyn also commanded the Auxiliary Cavalry Regiment, The Fife Mounted Rifle Volunteers from 1860 until his death in 1866.
Rosslyn was returned to Parliament for Dysart Burghs, in Fife, in 1830, a seat he held until 1831, and then represented Grimsby from 1831 to 1832. He succeeded his father in the earldom in 1837. In 1841 he was sworn of the Privy Council and appointed Master of the Buckhounds under Sir Robert Peel, which he remained until the government fell in 1846. He held the same office from February to December 1852 under Lord Derby, and was briefly Under-Secretary of State for War under Derby from March to June 1859.
Lord Rosslyn was also a Deputy Lieutenant for Fife.
In 1826, James married Frances Wemyss (1794–1858), daughter of Lt.-Gen. William Wemyss, of Wemyss Castle, Fife. Together, they were the parents of two sons and a daughter, including:
Lady Rosslyn died on 30 September 1858 and Lord Rosslyn died, several years later, in June 1866, aged 64. He was succeeded in the earldom by his only surviving son, Robert.[1]