| Honorific-Prefix: | The Right Honourable |
| The Viscount Ullswater | |
| Office1: | Speaker of the House of Commons of the United Kingdom |
| Term Start1: | 8 June 1905 |
| Term End1: | 28 April 1921 |
| Monarch1: | Edward VII George V |
| Primeminister1: | Arthur Balfour Henry Campbell-Bannerman H. H. Asquith David Lloyd George |
| Predecessor1: | Sir William Gully |
| Successor1: | J. H. Whitley |
| Office2: | Deputy Speaker of the House of Commons Chairman of Ways and Means |
| Term Start2: | 1895 |
| Term End2: | June 1905 |
| Monarch2: | |
| Predecessor2: | John William Mellor |
| Successor2: | Sir John Lawson |
| Office3: | Parliamentary Under-Secretary of State for Foreign Affairs |
| Term Start3: | 22 September 1891 |
| Term End3: | 18 August 1892 |
| Monarch3: | Victoria |
| Primeminister3: | The Marquess of Salisbury |
| Predecessor3: | Sir James Fergusson |
| Successor3: | Sir Edward Grey |
| Office5: | Member of Parliament for Penrith and Cockermouth |
| Term Start5: | 14 December 1918 |
| Term End5: | 13 May 1921 |
| Predecessor5: | constituency established |
| Successor5: | Cecil Lowther |
| Office6: | Member of Parliament for Penrith |
| Term Start6: | 27 July 1886 |
| Term End6: | 14 December 1918 |
| Predecessor6: | Henry Howard |
| Successor6: | constituency abolished |
| Office7: | Member of Parliament for Rutland |
| Term Start7: | 1 September 1883 |
| Term End7: | 18 December 1885 |
| Predecessor7: | Gerard Noel |
| Successor7: | George Finch |
| Office4: | Member of the House of Lords Lord Temporal |
| Term Start4: | 8 July 1921 |
| Term End4: | 27 March 1949 Hereditary Peerage |
| Predecessor4: | Peerage created |
| Successor4: | The 2nd Viscount Ullswater |
| Birth Date: | 1 April 1855 |
| Nationality: | British |
| Party: | Conservative |
| Alma Mater: | King's College London Trinity College, Cambridge |
| Spouse: | Mary Beresford-Hope (d. 1944) |
James William Lowther, 1st Viscount Ullswater, (1 April 1855 – 27 March 1949), was a British Conservative politician. He was Speaker of the House of Commons between 1905 and 1921. He was the longest-serving Speaker of the 20th century.
The son of Hon. William Lowther, a grandson of William Lowther, 1st Earl of Lonsdale, and for 25 years Member of Parliament for Westmorland, and Alice, 3rd daughter of James Parke, 1st Baron Wensleydale, Lowther was educated at Eton College, King's College London where he took an Associateship degree, and at Trinity College, Cambridge, where he studied classics and law. Lowther became a barrister in 1879, eventually becoming a Bencher of the Inner Temple in 1906.
He was Member of Parliament for Rutland in 1883; contested Mid Cumberland in 1885; and sat for Penrith from 1886 to 1921. He was appointed 4th Charity Commissioner in 1887, and held junior ministerial office as Parliamentary Under-Secretary of State for Foreign Affairs from 1891 to 1892. He was Chairman of Ways and Means and Deputy Speaker from 1895 to 1905 and Speaker of the House of Commons from 1905 to 1921.
Lowther represented Great Britain at the International Conference at Venice in 1892, and at the International Conference on Emigration at Rome in 1924. He was Chairman of the Speakers' Electoral Reform Conference in 1916–1917, of the Buckingham Palace Conference (on the partition of Ulster) in 1914, of the Boundary Commissions (Great Britain and Ireland) in 1917, of the Royal Commission on Proportional Representation in 1918, Devolution Conference in 1919, of the Royal Commission on London Government, 1921–1922; of Review Committee Political Honours, 1923–1924, and Statutory Commission on Cambridge University, 1923; of the Agricultural Wages Board from 1930 to 1940; of the Lords and Commons Committee on Electoral Reform, 1929–1930; and of BBC Enquiry Committee, 1935. He was a Trustee of the British Museum from 1922 to 1931 and a Trustee of the National Portrait Gallery from 1925. In 1907 his portrait was painted by Philip de László.
He was appointed to the Privy Council in 1898, created 1st Viscount Ullswater, of Campsea Ashe, in the County of Suffolk, on his retirement as Speaker in 1921, and appointed a Knight Grand Cross of the Order of the Bath (GCB) in July 1921. He also held the degrees of DCL from the University of Oxford, LL.D from the University of Cambridge and DCL from the University of Leeds.
| Crest: | A dragon passant Argent. |
| Escutcheon: | Or six annulets three two and one and in chief a crescent for difference all Sable. |
| Supporters: | On either side a horse Argent gorged with a wreath of laurel Vert and charged on the shoulder with a portcullis chained Or. |
| Motto: | Magistratum Indicat Virum (The Office Shows The Man)[1] |
On 1 March 1886, Lowther married Mary Frances Beresford-Hope (d. 16 May 1944). They had three children:
He was succeeded to the viscountcy by his great-grandson.