List of prime ministers of the United Kingdom by length of tenure
This article lists each Prime Minister of the United Kingdom in order of term length. This is based on the difference between dates; if counted by number of calendar days all the figures would be one greater.
Of the 55 Prime Ministers, nine served more than 10 years while seven have served less than a year.
Robert Walpole is the only person to have served as Prime Minister for more than two decades. George Canning served for less than four months before his death.
Ordered by tenure
In this table, "Terms in office" is the number of separate, discontiguous periods served as Prime Minister.| Rank | Prime Minister | Length served | Terms in office | Party | Start |
| 1 | Sir Robert Walpole | 20 years, 314 days | 1 | Whig | 1721 |
| 2 | William Pitt the Younger | 18 years, 343 days | 2 | Tory | 1783 |
| 3 | The Earl of Liverpool | 14 years, 305 days | 1 | Tory | 1812 |
| 4 | The Marquess of Salisbury | 13 years, 252 days | 3 | Conservative | 1885 |
| 5 | William Ewart Gladstone | 12 years, 126 days | 4 | Liberal | 1868 |
| 6 | Lord North | 12 years, 58 days | 1 | Tory | 1770 |
| 7 | Margaret Thatcher | 1 | Conservative | 1979 | |
| 8 | Henry Pelham | 10 years, 191 days | 1 | Whig | 1743 |
| 9 | Tony Blair | 1 | Labour | 1997 | |
| 10 | The Viscount Palmerston | 9 years, 141 days | 2 | WhigLiberal | 1855 |
| 11 | H. H. Asquith | 8 years, 244 days | 1 | Liberal | 1908 |
| 12 | Sir Winston Churchill | 8 years, 239 days | 2 | Conservative | 1940 |
| 13 | Harold Wilson | 7 years, 279 days | 2 | Labour | 1964 |
| 14 | The Duke of Newcastle | 7 years, 205 days | 2 | Whig | 1754 |
| 15 | Stanley Baldwin | 7 years, 82 days | 3 | Conservative | 1923 |
| 16 | Benjamin Disraeli | 6 years, 339 days | 2 | Conservative | 1868 |
| 17 | Ramsay MacDonald | 6 years, 289 days | 2 | LabourNational Labour | 1924 |
| 18 | Harold Macmillan | 6 years, 281 days | 1 | Conservative | 1957 |
| 19 | The Viscount Melbourne | 6 years, 255 days | 2 | Whig | 1834 |
| 20 | John Major | 1 | Conservative | 1990 | |
| 21 | Clement Attlee | 6 years, 92 days | 1 | Labour | 1945 |
| 22 | David Cameron | 1 | Conservative | 2010 | |
| 23 | Lord John Russell | 6 years, 11 days | 2 | WhigLiberal | 1846 |
| 24 | David Lloyd George | 5 years, 317 days | 1 | Liberal | 1916 |
| 25 | Sir Robert Peel | 5 years, 57 days | 2 | Conservative | 1834 |
| 26 | The Earl of Derby | 3 years, 280 days | 3 | Conservative | 1852 |
| 27 | Edward Heath | 3 years, 259 days | 1 | Conservative | 1970 |
| 28 | The Earl Grey | 3 years, 229 days | 1 | Whig | 1830 |
| 29 | Arthur Balfour | 3 years, 145 days | 1 | Conservative | 1902 |
| 30 | The Duke of Portland | 3 years, 82 days | 2 | WhigTory | 1783 |
| 31 | Henry Addington | 3 years, 54 days | 1 | Tory | 1801 |
| 32 | James Callaghan | 1 | Labour | 1976 | |
| 33 | Theresa May | 1 | Conservative | 2016 | |
| 34 | Neville Chamberlain | 2 years, 348 days | 1 | Conservative | 1937 |
| 35 | The Duke of Wellington | 2 years, 320 days | 2 | Tory | 1828 |
| 36 | Gordon Brown | 1 | Labour | 2007 | |
| 37 | Spencer Perceval | 2 years, 221 days | 1 | Tory | 1809 |
| 38 | Henry Campbell-Bannerman | 2 years, 122 days | 1 | Liberal | 1905 |
| 39 | George Grenville | 2 years, 85 days | 1 | Whig | 1763 |
| 40 | The Earl of Chatham | 2 years, 76 days | 1 | Whig | 1766 |
| 41 | The Earl of Aberdeen | 2 years, 42 days | 1 | Peelite | 1852 |
| 42 | Sir Anthony Eden | 1 year, 279 days | 1 | Conservative | 1955 |
| 43 | The Earl of Wilmington | 1 year, 119 days | 1 | Whig | 1742 |
| 44 | The Marquess of Rockingham | 1 year, 113 days | 2 | Whig | 1765 |
| 45 | The Earl of Rosebery | 1 year, 109 days | 1 | Liberal | 1894 |
| 46 | The Duke of Grafton | 1 year, 106 days | 1 | Whig | 1768 |
| 47 | The Lord Grenville | 1 year, 42 days | 1 | Whig | 1806 |
| 48 | Boris Johnson | ' ' | 1 | Conservative | 2019 |
| 49 | Sir Alec Douglas-Home | 363 days | 1 | Conservative | 1963 |
| 50 | The Earl of Bute | 317 days | 1 | Tory | 1762 |
| 51 | The Earl of Shelburne | 266 days | 1 | Whig | 1782 |
| 52 | The Duke of Devonshire | 225 days | 1 | Whig | 1756 |
| 53 | Bonar Law | 211 days | 1 | Conservative | 1922 |
| 54 | The Viscount Goderich | 144 days | 1 | Tory | 1827 |
| 55 | George Canning | 119 days | 1 | Tory | 1827 |