Spencer Compton Cavendish, 8th Duke of Devonshire (23 July,1833 - 24 March,1908) was a British politician, previously known (1858-1891) as Marquess of Hartington.

Cavendish was educated at Trinity College, Cambridge and entered Parliament in 1857. Between 1863 and 1874 Hartington held various Government posts, including lord of the Admiralty, under-secretary for war, postmaster-general, and chief secretary for Ireland. In 1875 he became Leader of the Liberal opposition, and in 1880, after the fall of Benjamin Disraeli's government, he was invited to form a government, but chose instead to serve under William Ewart Gladstone as Secretary of State for India (1880-1882) and Secretary of State for War (1882-1885). In 1886 he broke with Gladstone over Irish Home Rule, and became the leader of the Liberal Unionists. Queen Victoria asked him twice more in 1886-7 to form a government, but again he declined, giving support from the back benches to the Conservative government of Lord Salisbury. Devonshire eventually joined Salisbury's government in 1895 as Lord President of the Council. He resigned from the government in 1903, and from the Liberal Unionist Association the following spring, in protest at Joseph Chamberlain's Tariff Reform scheme.

|- style="text-align: center;" | width="30%" |Preceded by:
The Earl De Grey | width="40%" style="text-align: center;" |Secretary of State for War
1866 | width="30%" |Succeeded by:
Jonathan Peel

|- style="text-align: center;" | width="30%" |Preceded by:
The Duke of Montrose | width="40%" style="text-align: center;" |Postmaster-General
1868–1871 | width="30%" |Succeeded by:
William Monsell

|- style="text-align: center;" | width="30%" |Preceded by:
Chichester Fortescue | width="40%" style="text-align: center;" |Chief Secretary for Ireland
1871–1874 | width="30%" |Succeeded by:
Sir Michael Hicks-Beach

|- style="text-align: center;" | width="30%" |Preceded by:
William Ewart Gladstone | width="40%" style="text-align: center;" |Leader of the British Liberal Party
co-equal with The Earl Granville
1875–1880 | width="30%" |Succeeded by:
William Ewart Gladstone

|- style="text-align: center;" | width="30%" |Preceded by:
The Viscount Cranbrook | width="40%" style="text-align: center;" |Secretary of State for India
1880–1882 | width="30%" |Succeeded by:
The Earl of Kimberley

|- style="text-align: center;" | width="30%" |Preceded by:
Hugh Childers | width="40%" style="text-align: center;" |Secretary of State for War
1882–1885 | width="30%" |Succeeded by:
William Henry Smith

|- style="text-align: center;" | width="30%" |Preceded by:
(none) | width="40%" style="text-align: center;" |Leader of the Liberal Unionist Association
1886–1903 | width="30%" |Succeeded by:
Joseph Chamberlain

|- style="text-align: center;" | width="30%" |Preceded by:
The Earl of Rosebery | width="40%" style="text-align: center;" |Lord President of the Council
1895–1903 | width="30%" |Succeeded by:
The Marquess of Londonderry

|- style="text-align: center;" | width="30%" |Preceded by:
The Marquess of Salisbury | width="40%" style="text-align: center;" |Leader of the House of Lords
1902–1903 | width="30%" |Succeeded by:
The Marquess of Lansdowne