On 7 January 1746 he was born at Elphinstone Tower, near Stirling, and named after his great-uncle George Keith, last Earl Marischal. In 1761 he entered the navy. From 1781 till 1790 he was a Whig M.P. for Dunbarton. On 9 April 1787, he married Jane Mercer and they became the parents of one daughter but, on 12 December 1789, his wife died.
He became Treasurer and Comptroller of the Household to the Duke of Clarence, the future King William IV. In 1793 he distinguished himself against the French off Toulon and, on 13 April 1794, became a Knight of the Bath. In 1794 he became a Rear Admiral and, in 1795, a Vice Admiral.

He commanded the expedition to Cape Town, which place capitulated on 17 September 1795, while the Dutch fleet at Saldanha Bay surrendered to him in August 1796. For this he was rewarded by being created Baron Keith of Stonehaven Marischal, in the Irish peerage, with a special remainder, failing heirs male of his body, to his daughter Margaret.
As Commander at Sheerness he quelled the alarming mutiny at the Nore. From 1796 till 1801 he was a Whig M.P. for Stirling. From 1799 till 1802, he was also Commander-in-Chief in the Mediterranean, aiding in the operations at Aboukir Bay and the capture of Alexandria. On 15
December 1801, he was rewarded with a British peerage of the same designation. In 1801 he became an Admiral of the Blue and, in 1805, of the White. 
On 10 January 1808 he married Hester Maria Thrale and another daughter was born. In 1810 he became an Admiral of the Red. In 1812 he was the Commander of the Channel Fleet and conducted the correspondence with Napoleon Bonaparte in regards to his banishment to St. Helena. Having received many decorations, on 1 June 1814 he was created Viscount Keith. On 10 March 1823 he died at Tullyllan, on the Firth of Forth, and was buried there.
 

Source: Leo van de Pas