He was the son of John Douglas, descended from James Douglas, minister of Glenbervie in Aberdeenshire, son of Sir Archibald Douglas and half-brother of William Douglas, 9th Earl of Angus. His mother was Margaret Gordon, daughter and co-heir of James Gordon, of Fechel.^[1] His sister Katherine married James Mercer, army officer and poet.^[2]

Douglas was educated at the University of Aberdeen, graduating MA in 1765 and then studied both Law and Medicine at the University of Leyden. He was admitted to Lincoln's Inn in London in 1771, was called to the Bar in 1776 and became King's Counsel in 1793.^[3]

The same year he was appointed a King's Counsel Douglas gave up his legal career on his appointment as Chief Secretary for Ireland under William Pitt the Younger.^[4] In 1794 he was admitted to both the Irish^[5] and English Privy Council^[6] and returned to the Irish House of Commons for St Canice,^[7] a seat he held until 1796. In 1795 he was elected to the British House of Commons for Fowey.^[8] He later represented Midhurst between 1796 and 1800,^[9] Plympton Erle between 1801 and 1802^[10] and Hastings between 1802 and 1806.^[11]

He was asked to accompany Earl Macartney to the Cape of Good Hope in 1796 and, after 18 months there, to succeed him as governor. His wife did not like the idea and he declined the offer, even though an Irish peerage had also been offered.^[12] In 1797 Douglas was made a Lord of the Treasury by Pitt,^[13] In 1800 Douglas was asked for a second time to go to the Cape as governor.^[14] He finally agreed in October 1800, again for an Irish peerage and was so appointed Governor of the Cape of Good Hope,^[15] Douglas changed his mind again and accepted a post as Joint Paymaster of HM Forces, subsequently receiving £2731. 10s. in salary, paid from the Cape Treasury, even though he never went there.^[16] At the end of the year on 29 November 1800 he was created Baron Glenbervie, of Kincardine, in Scotland.^[17]

After serving as joint Paymaster of the Forces between 1801 and 1803^[18] and Vice-President of the Board of Trade between 1801 and 1804,^[19] he was Surveyor General of Woods, Forests, Parks, and Chases between 1803 and 1806^[20] and 1807 and 1810. On the office of the Surveyor General of the Land Revenues of the Crown being combined with the former in 1810, became the First Commissioner of Woods and Forests, the head of the new department. He held the office until 1814.

In 1789 Lord Glenbervie married Lady Catherine Anne, eldest daughter of Frederick North, Lord North.^[21] Their only son Frederick Douglas sat as Member of Parliament for Banbury between 1812 and his early death in 1819.^[22] Lady Glenbervie died in February 1817, aged 56. Glenbervie survived her by six years and died in May 1823, aged 79. As he had no surviving male issue the barony became extinct on his death.^[21] His library was sold by R. H. Evans in London in two parts, on 13 June 1823 (and seven following days) and 5 July 1823 (and six following days; copies of the catalogue are at Cambridge University Library (shelfmark Munby.c.126(11) and Munby.c.126(13)).

In 1795 he was elected a Fellow of the Royal Society of London^[23] and in 1806 elected a Fellow of the Royal Society of Edinburgh, when his proposers were Allan Maconochie, Lord Meadowbank, Gilbert Innes and John Playfair.^[24]

• Hansard 1803–2005: contributions in Parliament by Sylvester Douglas
• "Archival material relating to Douglas, Sylvester (1743–1823) Baron Glenbervie, politician". UK National Archives.