Baron Merthyr, of Senghenydd in the County of Glamorgan,^[1] is a title in the Peerage of the United Kingdom. It was created in 1911 for the Welsh coal mining magnate Sir William Lewis, 1st Baronet. He had already been created a baronet, of Nantgwyne in the County of Glamorgan, in 1896.^[2] The barony is named after the town of Merthyr Tydfil, where Lewis was born. Lord Merthyr's grandson, the third Baron, was Chairman of Committees in the House of Lords from 1957 to 1965 and a Deputy Speaker from 1957 to 1974. The latter was succeeded by his son, the fourth Baron. He disclaimed the peerage for life on 26 April 1977,^[3] three weeks after succeeding his father. He did not use his title of baronet either. He died on 5 August 2015.^[4]

The Hon. Robin Lewis, fourth son of the third Baron, was appointed Lord Lieutenant of Dyfed in December 2006, although this was not officially reported in the London Gazette until September 2007.

• William Thomas Lewis, 1st Baron Merthyr (1837–1914)
• Herbert Clark Lewis, 2nd Baron Merthyr (1866–1932)
• William Brereton Couchman Lewis, 3rd Baron Merthyr (1901–1977)
• Trevor Oswin Lewis, 4th Baron Merthyr (1935–2015) (disclaimed 1977)
• David Trevor Lewis, 5th Baron Merthyr (born 1977)

The heir presumptive is the present holder's uncle, Peter Herbert Lewis (born 1937).

Coat of arms of Baron Merthyr

Crest An eagle displayed Azure charged on the breast with a bee volant Or and holding in the beak a roll of paper Argent. Escutcheon Sable a lion rampant Argent overall a fess Or charged with three bees volant Proper. Supporters Dexter and sinister, a lion rampant Sable charged on the shoulder with a bezant thereon a bee volant Proper. Motto 1st Gwna A Ddylit Doed A Ddel 2nd Hirbarhad.[5]

• Hesilrige, Arthur G. M. (1921). Debrett's Peerage and Titles of courtesy. London: London: Dean & son, limited. p. 626.
• Dod's peerage, Baronetage, Knightage etc. Of Great Britain and Ireland, 1915. 12 Mitre Court Chambers Temple, London, UK: London : Simkin, Marshall, Hamilton, Kent. 21 April 2016 [1918]. p. 386. Charles Dod((cite book)): CS1 maint: location (link)
• Kidd, Charles, Williamson, David (editors). Debrett's Peerage and Baronetage (1990 edition). New York: St Martin's Press, 1990, ^{[page needed]}
• Leigh Rayment's Peerage Pages ^{[self-published source] [better source needed]}

v t e Extant hereditary baronies in the Peerage of the United Kingdom
King George III	Ellenborough Manners
The Prince Regent	Churchill Harris
King George IV	Ravensworth Delamere Forester Rayleigh Gifford Feversham Seaford Plunket Heytesbury Skelmersdale Wynford
King William IV	Kilmarnock Poltimore Mostyn de Saumarez Denman Abinger Ashburton Hatherton Stratheden Lovat^*
Queen Victoria	Rossmore^• Carew^• de Mauley Wrottesley Sudeley Methuen Stanley of Alderley^• Leigh Monteagle of Brandon Campbell Vivian Congleton Eddisbury^• Londesborough de Freyne Raglan Belper Chesham Churston Leconfield Lyveden Brougham and Vaux Westbury Annaly Northbrook Hartismere^• Hylton Penrhyn O'Neill Napier of Magdala Dunning^* Acton Wolverton O'Hagan Sandhurst Ettrick^* Aberdare Moncreiff Coleridge Cottesloe Hampton Harlech Tollemache Gerard Sackville Norton Trevor Ampthill Derwent Hothfield Tennyson Strathspey Monk Bretton Northbourne Northington^• Rothschild Revelstoke Monkswell Ashbourne St Oswald Montagu of Beaulieu Elphinstone^* Hindlip Grimthorpe Kensington^• Hamilton of Dalzell St Levan Basing de Ramsey Addington Savile Ashcombe Crawshaw Amherst of Hackney Newton Dunleath Swansea Aldenham HolmPatrick Burton Glanusk Cranworth Avebury Killanin Strathcona and Mount Royal
King Edward VII	Kinross Shuttleworth Grenfell Redesdale Burnham Biddulph Ritchie of Dundee Hemphill Joicey Nunburnholme Swaythling Blyth Marchamley Gorell Fisher Kilbracken
King George V	Hardinge of Penshurst de Villiers Glenconner Aberconway Merthyr Rowallan Ashton of Hyde Ravensdale Hollenden Parmoor Cunliffe Wrenbury Faringdon Shaughnessy Rathcreedan Somerleyton Carnock Beaverbrook Gainford Forteviot Colwyn Gisborough Morris Cawley Terrington Glenarthur Phillimore Inverforth Sinha Cochrane of Cults Clwyd Russell of Liverpool Swinfen Meston Cullen of Ashbourne Trevethin Glendyne Manton Forres Vestey Borwick Maclay Bethell Hunsdon Darling Banbury of Southam Merrivale Bradbury Mereworth^• Greenway Hayter Cornwallis Daresbury Wraxall Remnant Moynihan Craigmyle Dulverton Luke Alvingham Baden-Powell Ponsonby of Shulbrede Dickinson Noel-Buxton Howard of Penrith Rochester Selsdon Moyne Davies Rankeillour Brocket Milne Rennell Mottistone Iliffe Palmer Rockley Elton Wakehurst Hesketh Tweedsmuir Wigram Riverdale May Kennet Strathcarron
King Edward VIII	Catto
King George VI	Windlesham Mancroft McGowan Denham Rea Cadman Kenilworth Pender Roborough Brassey of Apethorpe Stamp Bicester Milford Hankey Harmsworth Rotherwick Glentoran Tryon Croft Teviot Nathan Reith Kindersley Ironside Latham Wedgwood Geddes Bruntisfield Brabazon of Tara Keyes Hemingford Moran Killearn Dowding Gretton Westwood Hazlerigg Hacking Chetwode Sandford Altrincham Broadbridge Mountevans Lindsay of Birker Piercy Chorley Calverley Tedder Colgrain Darwen Lucas of Chilworth Shepherd Newall Oaksey Rugby Layton Simon of Wythenshawe Kershaw Trefgarne Crook Amwell Milverton Clydesmuir Burden Haden-Guest Silkin§ Hives Ogmore Morris of Kenwood Macpherson of Drumochter Kenswood Freyberg Milner of Leeds Kirkwood Wise
Queen Elizabeth II	Jeffreys Rathcavan Baillieu Grantchester Coleraine Harvey of Tasburgh Gridley Strathalmond Strathclyde Clitheroe McNair Colyton Astor of Hever Sinclair of Cleeve Bridges Norrie Birkett Harding of Petherton Poole Rootes Netherthorpe Crathorne Spens MacAndrew Nelson of Stafford Howick of Glendale Sanderson of Ayot Cobbold Robertson of Oakridge Marks of Broughton Fairhaven Leighton of St Mellons Brain Aldington Inchyra Silsoe Egremont Thomson of Fleet Martonmere Sherfield Inglewood Glendevon Grimston of Westbury Renwick St Helens Margadale
§: Disclaimed.  Italics: This title is held by a peer who holds another of higher precedence. ^* Also a Lord in the Peerage of Scotland  ^• Also a Baron in the Peerage of Ireland