| Lonetree Limited | Hospitality | 1998 |
| Loomzen Limited | Wholesale & retail | 2025 |
| Lorenzo's Bistro Ltd | Hospitality | 2019 |
| Love Thai Food (UK) Limited | Hospitality | 2023 |
| Love Thai Massage (UK) Limited | Other services | 2023 |
| Lowcho Ltd | Manufacturing | 2021 |
| LSJ Building & Construction Limited | Construction | 2017 |
| LT Nail Bar 7 Ltd | Other services | 2024 |
| Luna Properties Pembrokeshire Limited | Construction | 2025 |
| Lutece Farm Ltd | Agriculture & fishing | 2021 |
| LW Pro Build Ltd | Construction | 2026 |
| Lydstep Assessment Ltd | Education | 2024 |
| Lydstep Training Ltd | Education | 2024 |
| Lyfli Foods Ltd | Manufacturing | 2017 |
| LYG Properties Ltd | Real estate | 2025 |
| M & D Care Gowerton Limited | Administrative & support | 2024 |
| M & D Care Operations Limited | Health & social care | 2022 |
| M & D Care Pontardawe Limited | Administrative & support | 2024 |
| M & D Care Rhigos Limited | Administrative & support | 2024 |
| M & D Care Supported Living Limited | Administrative & support | 2023 |
| M & D Care Tonypandy Limited | Administrative & support | 2024 |
| M D Plant & Tractor Sales Ltd | Wholesale & retail | 2021 |
| M G Thomas & Sons Ltd | Transport & logistics | 2024 |
| M Howells Plumbing & Heating Ltd | Construction | 2015 |
| M I Haslam Carpentry and Building Contractors Ltd | Construction | 2011 |
| M J W Pensions & Investments Limited | Financial services | 2017 |
| M O S Security Consultancy Limited | Administrative & support | 2025 |
| M Plant Hire Ltd | Administrative & support | 2023 |
| M T Lloyd Maintenance Limited | Construction | 2015 |
| M.A.L.D. Energy Ltd | Energy | 2014 |
| M.B.H.3 Developments Limited | Construction | 2020 |
| M.B.H.3 Limited | Real estate | 1992 |
| M.T Supplies (Wales) Ltd | Wholesale & retail | 2019 |
| MA & IA Catering Ltd | Hospitality | 2025 |
| MA Lettings Ltd | Real estate | 2017 |
| MAA Stores Limited | Wholesale & retail | 2022 |
| Mabiko Ltd | Hospitality | 2024 |
| Macduff Robotics Ltd | Manufacturing | 2022 |
| Maes Cochen Management Company Limited | Households | 2025 |
| Maescowin Ltd | Agriculture & fishing | 2017 |
| Maesiago Limited | Construction | 2018 |
| Maeslan Farm Limited | Agriculture & fishing | 2020 |
| Maesyramaeth CYF | Agriculture & fishing | 2025 |
| Mageed Medical Trading Enterprises Limited | Health & social care | 2022 |
| Magnum Hospitality Limited | Hospitality | 2026 |
| Magnus Simul Limited | Construction | 2017 |
| Maidenhead Air Systems Limited | Construction | 2005 |
| Make and Mend Workshop C.I.C. | Other services | 2024 |
| Making Way Marine Training Limited | Education | 2012 |
| Malcolm Optometry Service Limited | Health & social care | 2016 |
| Malda Advisory Ltd | Professional & scientific | 2026 |
| Malthouse Antiques Ltd | Wholesale & retail | 2022 |
| Mamgus Kitchen Limited | Hospitality | 2025 |
| Mane Academy Ltd | Other services | 2023 |
| Mansel Street Dental Laboratory Ltd | Health & social care | 2017 |
| Mansion House Llansteffan Ltd | Hospitality | 2012 |
| Manufacturing Health Limited | Health & social care | 2016 |
| Maokro Ltd | Professional & scientific | 2023 |
| Maple Leaf Rigging Limited | Information & communication | 2023 |
| Marchnad Ffermwyr Talog C.I.C. | Wholesale & retail | 2024 |
| Mares Landscaping Ltd | Administrative & support | 2025 |
| Mari Lwyd Film Ltd | Information & communication | 2025 |
| Mark Williams Carpets Limited | Construction | 2026 |
| Marketa Projects PC | | 2019 |
| Marlingham Limited | Financial services | 1993 |
| Marric Developments Limited | Construction | 2001 |
| Marsh Stores Limited | Wholesale & retail | 2008 |
| Martin Waterworth Limited | Professional & scientific | 2002 |
| Masonpoint Developments Limited | Real estate | 2026 |
| Mathias Renovations Ltd | Construction | 2021 |
| Matt Giles Sports Medicine Limited | Health & social care | 2023 |
| Matthew Jones ( Wales ) Limited | Construction | 2017 |
| Matthew L Jones Ltd | Other services | 2014 |
| Maverick's of Tenby Ltd | Other services | 2016 |
| Mawrth Mier Services Ltd | Extraterritorial | 2015 |
| MB Web Design Ltd | Information & communication | 2015 |
| MBD Professional Limited | Real estate | 2022 |
| Mbee FEA Limited | Professional & scientific | 2019 |
| Mbgreen Ltd | Wholesale & retail | 2022 |
| Mcbro Property Investments Ltd | Real estate | 2013 |
| MCD999 Limited | Professional & scientific | 2024 |
| Mcmahon Property Group Limited | Real estate | 2025 |
| MCW Group Limited | Financial services | 2023 |
| Meadow Farm Tenby Ltd | Hospitality | 2014 |
| Medispace Carmarthen Ltd | Real estate | 2024 |
| Medocoaches Ltd | Education | 2025 |
| Megneli Estates Ltd | Real estate | 2023 |
| MEI Consulting Ltd | Information & communication | 2016 |
| Meithrinfa Dechrau Disglair Ltd | Health & social care | 2024 |
| Meithrinfa Liliwenfach Nursery Ltd | Education | 2014 |
| Mekatek Limited | Manufacturing | 1985 |
| Melin Assessments Limited | Professional & scientific | 2023 |
| Melin-Y-Derw Limited | Manufacturing | 2012 |
| Melmark Limited | Professional & scientific | 2010 |
| Melyn Pictures Ltd | Information & communication | 2021 |
| MEN2MEN Network CIC | Public administration | 2022 |
| Menolink LLP | | 2024 |
| Mental Health SIR GAR Ltd | Health & social care | 2023 |
| Mentrau Creadigol Cymru CYF | Real estate | 2017 |
| Merlin Bushcraft Limited | Education | 2018 |