He was the son of the Honorary James Wemyss, third son of the 5th Earl of Wemyss, and his wife Lady Elizabeth, only daughter of the 17th Earl of Sutherland. On 16 September 1788 he married Frances, daughter of Sir William Erskine, 1st Baronet.
Their children included
Frances (1794–1858), who married James Street Clair-Erskine, 3rd Earl of Rosslyn;
James Erskine Wemyss (1789–1854), a Rear-Admiral. And
William Wemyss (1790–1852), also a Lieutenant-General. Both sons married daughters of William Hay, 17th Earl of Erroll.
From 1784 to 1787 Wemyss was Member of Parliament for Sutherland, succeeding his father, before sitting for Fife from 1787 to 1796 and again from 1807 to 1820.
Captain in the Army by brevet, 1 July 1783 DAG in Scotland and Major, 18 November 1786 DAG in Scotland and Lieutenant-Colonel, 1 October 1791 Colonel, 22 August 1795
Action near Ardee
On 16 September 1800 he was Colonel of a new Regiment of Infantry, later the 93rd Regiment of Foot. On 30 October 1805 he was promoted to lieutenant-general.
He was aide-de-camp to Major-General Sir William Erskine in the 1809 Walcheren Campaign and during the Peninsular War. In 1810 it was announced that he would succeed Sir Hew Dalrymple as Colonel of the 37th (North Hampshire) Regiment of Foot, with General Needham becoming Colonel of the 93rd, but the appointments did not take place and Wemyss remained Colonel of the 93rd Foot until his death, when he was succeeded by Sir Thomas Hislop.
He did however gain a promotion to full general on 4 June 1814.
Wemyss died on 4 February 1852 at his home in Cumberland Lodge, Windsor Great Park after a "lingering and distressing illness". He is buried in a railed enclosure in Street Mary"s Churchyard, Wimbledon, London.
4th United Kingdom Parliament. 5th United Kingdom Parliament. 6th United Kingdom Parliament.
16th Parliament of Great Britain.
17th Parliament of Great Britain.
