| Lotus Property Management Limited | Real estate | 2005 |
| Lounges@Tmcw Ltd | Hospitality | 2022 |
| Lovesgrove Management Company Ltd | Households | 2001 |
| Lssk Developments Limited | Real estate | 2024 |
| LT Property Management Limited | Households | 2018 |
| LT Technical Productions Ltd | Arts & recreation | 2025 |
| Luke Evans Construction Ltd | Construction | 2023 |
| M & B Markets Ltd | Real estate | 2014 |
| M Davies Plumbing & Heating Ltd | Construction | 2016 |
| M F Healy Ltd | Professional & scientific | 2022 |
| M G Corner Shop Ltd | Wholesale & retail | 2023 |
| M L Landscapes & Garden Services LP | | 2018 |
| M L Landscapes Limited | Administrative & support | 2017 |
| M P Evans Plumbing Ltd | Construction | 2022 |
| M R WOW Limited | Hospitality | 2025 |
| M S Properties (UK) Limited | Real estate | 2013 |
| M S Verman Ltd | Wholesale & retail | 2026 |
| M T Byrne Ltd | Construction | 2006 |
| Mabis CYF | Professional & scientific | 2005 |
| Mach Recordings Limited | Information & communication | 2021 |
| MACH1 Leisure Limited | Hospitality | 2012 |
| Macken Rope Access Ltd | Construction | 2013 |
| Maesbangor Caravan Sales Limited | Other services | 2016 |
| Maesydderwen Developments Ltd | Real estate | 2006 |
| Mair Williams Cyfyngedig | Professional & scientific | 2013 |
| Manley & Colwell Auctions Ltd | Wholesale & retail | 2025 |
| Manoj Kulshrestha Limited | Health & social care | 2015 |
| Marches Forestry Services Ltd | Agriculture & fishing | 2021 |
| Mark Joseph Holdings Ltd | Financial services | 2024 |
| Matador Seminars Ltd | Wholesale & retail | 2025 |
| Matthews Property Development Limited | Construction | 2010 |
| Maveco Stone Machinery Limited | Wholesale & retail | 2014 |
| MCS Enviroculture Ltd | Professional & scientific | 2017 |
| Medically Enlightened Limited | Health & social care | 2025 |
| Medina Aberystwyth Limited | Hospitality | 2016 |
| Medina Restaurant Holdings Limited | Hospitality | 2022 |
| Medula Limited | Wholesale & retail | 2019 |
| Meduni Limited | Health & social care | 2025 |
| Meithrinfeydd Cymru CYF | Education | 2001 |
| MEM Aberystwyth Ltd | Administrative & support | 2003 |
| MEM Developments (Wales) Ltd | Construction | 2023 |
| Mens Dressing Gowns Limited | Wholesale & retail | 2014 |
| Menter a Busnes CYF | Administrative & support | 2024 |
| Menter Aberystwyth | Administrative & support | 2004 |
| Menter Cymunedol Mynach Cyfyngedig | Arts & recreation | 2015 |
| Menter Gymunedol Bronant Cyfyngedig | Hospitality | 1996 |
| Mep-Wales Ltd | Construction | 2023 |
| Mercator Rhyngwladol / Mercator International Ltd | Information & communication | 2018 |
| Merlin Homes Properties Limited | Administrative & support | 2009 |
| Mesen LAS CYF | Real estate | 2018 |
| Military Regalia Company Ltd | Wholesale & retail | 2012 |
| Mind Aberystwyth | Health & social care | 2004 |
| Ministry of Luxury Ltd | Wholesale & retail | 2025 |
| Mint Productions Ltd | Hospitality | 2026 |
| ML Concepts Ltd | Arts & recreation | 2025 |
| MMF Medical Limited Limited | Health & social care | 2022 |
| Moalom Limited | | 2015 |
| Modular Propulsion Limited | Manufacturing | 2014 |
| Modurdy Eiddwen Garage Ltd | Wholesale & retail | 2026 |
| Moduron Delfryn Owens Motors Limited | Extraterritorial | 2023 |
| Moldani Group Limited | Financial services | 2021 |
| Monticello Properties Ltd | Real estate | 2017 |
| Montrose Properties Limited | Construction | 1972 |
| Morgan & Flynn Ltd | Professional & scientific | 2022 |
| Morgans Developments Ltd | Construction | 2023 |
| Morgans Holdings Limited | Other services | 2016 |
| Morgans Properties Ltd | Real estate | 2009 |
| Morris and Bates Limited | Professional & scientific | 2010 |
| MR Fixit Heating Ltd | Construction | 2022 |
| Mslgnl Ltd | Health & social care | 2024 |
| Mudiad Meithrin CYF | Education | 1987 |
| Mumbeam’S Art Cafe Ltd | Wholesale & retail | 2025 |
| Mutant Caterpillar Games Limited | Wholesale & retail | 2009 |
| MW Scaffolding Holdings Ltd | Construction | 2018 |
| MW Scaffolding Limited | Construction | 1997 |
| My CPD Pilot Ltd | Information & communication | 2026 |
| My Nutrition Club Limited | Information & communication | 2025 |
| Mycrowd.Life Ltd | Information & communication | 2025 |
| Mykola's Autorepairs Limited | Wholesale & retail | 2026 |
| Mynydd Bach Bookkeeping Ltd | Administrative & support | 2016 |
| Mynydd Construction Ltd | Construction | 2023 |
| Nails Room by Hanna Limited | Wholesale & retail | 2026 |
| Nantllan Rentals Limited | Real estate | 2003 |
| Napier (2017) Limited | Households | 2017 |
| Nathan Davies Limited | Professional & scientific | 2022 |
| Natures RAW Ltd | Wholesale & retail | 2019 |
| Nedukas Anaesthetics Limited | Health & social care | 2010 |
| Needle Rock Ltd | Manufacturing | 2013 |
| Neil Wilkin Ltd | Manufacturing | 2021 |
| Nellie Technologies Limited | Professional & scientific | 2022 |
| Netsworkuk Ltd | Construction | 2026 |
| Neurabotics Ltd | Manufacturing | 2023 |
| Newbery and Daughters Ltd | Real estate | 2021 |
| News Mill Ltd | Professional & scientific | 2019 |
| Newsplan 2000 | Arts & recreation | 2000 |
| NI TRI Limited | Hospitality | 2008 |
| Nitavita Limited | Wholesale & retail | 2022 |
| Noblehairandbeauty Ltd | Other services | 2022 |
| Norit Properties Limited | Construction | 1960 |
| O R Griffiths CYF | Health & social care | 2025 |