[1] From 1784 to 1787 Wemyss was MP for Sutherland, succeeding his father,[2] before sitting for Fife from 1787 to 1796 and again from 1807 to 1820.

[3] Captain in the Army by brevet, 1 July 1783[4] DAG in Scotland and Major, 18 November 1786[5] DAG in Scotland and Lieutenant-Colonel, 1 October 1791[6] Colonel, 22 August 1795[7] He attained the rank of Major-General on 23 June 1798.

General Wemyss lined up the young men of each parish and invited them to drink from a large silver bound horn, having drunk his dram it was understood he consented to join the Regiment.

He was aide-de-camp to Major-General Sir William Erskine in the 1809 Walcheren Campaign and during the Peninsular War.

[17] On 16 September 1788[18] he married Frances, daughter of Sir William Erskine, 1st Baronet.