| Honorific-Prefix: | Colonel The Right Honourable |
| The Lord Llewellin | |
| Office: | 1st Governor-General of the Federation of Rhodesia and Nyasaland |
| Term Start: | 4 September 1953 |
| Term End: | 24 January 1957 |
| Primeminister: | Viscount Malvern Sir Roy Welensky |
| Predecessor: | Office established |
| Successor: | Sir Robert Clarkson Tredgold |
| Office2: | Minister of Aircraft Production |
| Primeminister2: | Winston Churchill |
| Term Start2: | 22 February 1942 |
| Term End2: | 22 November 1942 |
| Predecessor2: | The 1st Baron Brabazon of Tara |
| Successor2: | Sir Stafford Cripps |
| Office3: | President of the Board of Trade |
| Primeminister3: | Winston Churchill |
| Term Start3: | 4 |
| Term End3: | 22 February 1942 |
| Predecessor3: | Sir Andrew Duncan |
| Successor3: | Hugh Dalton |
| Office4: | Member of Parliament for Uxbridge |
| Term Start4: | 30 May 1929 |
| Term End4: | 15 June 1945 |
| Predecessor4: | Sir Dennistoun Burney, Bt |
| Successor4: | Frank Beswick |
| Birth Date: | 6 February 1893 |
| Party: | Conservative |
John Jestyn Llewellin, 1st Baron Llewellin (6 February 1893 – 24 January 1957) was a British army officer, Conservative Party politician and minister in Winston Churchill's war government.
Llewellin was the son of William Llewellin, of Upton House, Dorset, and Frances Mary, daughter of L. D. Wigan. He was educated at Eton.
Llewellin was commissioned into the Royal Garrison Artillery in 1914 and reached the rank of major during the First World War, winning the Military Cross in 1917. He remained in the Territorial Army after the war and was promoted to lieutenant-colonel commanding the Dorset Heavy Brigade in 1932.
He was promoted colonel in 1936 and retired in 1938. He was appointed an Officer of the Order of the British Empire (OBE) in 1926, promoted to a Commander (CBE) in 1939, and then was made a Knight Grand Cross (GBE) in 1953.
Llewellin was elected Member of Parliament (MP) for Uxbridge in Middlesex in 1929. He held a number of ministerial posts in the Coalition government, eventually serving as President of the Board of Trade for two weeks in 1942. He subsequently became Minister of Aircraft Production until replaced by Sir Stafford Cripps in November 1942. Later, Llewellin served on the Combined Policy Committee set up by the British and United States governments under the Quebec Agreement of 1943 to oversee the construction of the atomic bomb.
In December 1943, Llewellin's seat on the committee was assumed by Sir Ronald Campbell and Llewellin became Minister of Food, the position he held until the Churchill government fell to the Labour Party of Clement Attlee in July 1945. Llewellin lost his seat in the election and was raised to the peerage as Baron Llewellin, of Upton in the County of Dorset. After the war he served as Governor General of the Federation of Rhodesia and Nyasaland between 1953 and his death in January 1957.
Lord Lewellin died in January 1957, aged 63. The barony became extinct with his death.
| Escutcheon: | Gules three chevronels couped Ermine between as many spear heads Or. |
| Crest: | A lamb passant Argent supporting with the dexter forefoot a flagstaff in bend sinister Proper therefrom flowing a banner Gules charged with a spear head Or between two wings of the third on each a like spear head. |
| Supporters: | Dexter a farmer holding in the exterior hand a hay-fork; sinister an officer of the Merchant Navy holding in the exterior hand a pair of binoculars all Proper. |
| Motto: | Duw Fo Ar Fy Rhan [1] |