| Made From Love Ltd | Professional & scientific | 2025 |
| Madhatterz Play Centre Ltd. | Arts & recreation | 2018 |
| MAG - Swansea Ltd | Hospitality | 2024 |
| Magic Scissors ( Neath ) Ltd | Other services | 2021 |
| Magnolia Health and Wellbeing Ltd | Other services | 2017 |
| Mahler Limited | Administrative & support | 2017 |
| Mains Martial Arts Limited | Arts & recreation | 2022 |
| MAJ Design Ltd | Administrative & support | 2024 |
| Makepeace-Jones Property Ltd. | Real estate | 2025 |
| Mancuso Holdings Group Ltd | Financial services | 2023 |
| Mancuso Investment Group Ltd | Real estate | 2023 |
| Mane-Tamed Barbers Limited | Other services | 2018 |
| Manor Nest Ltd | Real estate | 2025 |
| Marbo Ltd | Professional & scientific | 2025 |
| Margetson Ltd | Real estate | 2024 |
| Marine Power Support Ltd | Manufacturing | 2024 |
| Mario's Flavours Ltd | Hospitality | 2024 |
| Mark Watts Holdings Limited | Financial services | 2025 |
| Marsh DP Ltd | Health & social care | 2021 |
| Marshall MAY Limited | Construction | 2011 |
| Martaban Family Rentals Limited | Real estate | 2025 |
| Marvmedia Ltd | Professional & scientific | 2023 |
| Massimo SFX Limited | Information & communication | 2013 |
| MAX Rocks Ltd | Manufacturing | 2019 |
| Mcdyer Control Systems Ltd | Manufacturing | 2009 |
| Mclem Group Ltd | Real estate | 2024 |
| MD Plumbing & Bathroom Co Ltd | Construction | 2022 |
| MDG Solutions Limited | Information & communication | 2019 |
| Meadows Farm Holiday Lets Ltd | Hospitality | 2024 |
| Meadows Holiday Lets (Gower) Ltd | Hospitality | 2026 |
| Meadows L&P Ltd | Real estate | 2026 |
| Mechatronics Systems Wales Ltd | Manufacturing | 2020 |
| Mechsig Ltd | Administrative & support | 2026 |
| Media Eclipse Ltd | Information & communication | 2007 |
| Medic Training Limited | Health & social care | 2014 |
| Medical Security Water Events (MSW) Ltd | Administrative & support | 2025 |
| Mega Skips Limited | Water & waste | 2024 |
| Melin Community Trust | Other services | 2002 |
| Melita Nursery Estates Ltd | Real estate | 2025 |
| Melody Wholesale Limited | Wholesale & retail | 2025 |
| Melyn Supermarket Ltd | Wholesale & retail | 2025 |
| Menter (2025) Cyfyngedig | Administrative & support | 2025 |
| Merlin Bros Properties Limited | Real estate | 2025 |
| Merlins Court Management Company (2015) Limited | Hospitality | 2015 |
| Merthyr Biomass Ltd | Energy | 2017 |
| Mesotreat Limited | Wholesale & retail | 2017 |
| Meta Roofing Solutions Ltd | Construction | 2025 |
| Meurig Investments Limited | Financial services | 2025 |
| MG M&E Ltd | Construction | 2014 |
| MH Land Intelligence Limited | Professional & scientific | 2025 |
| Mhum Ltd | Health & social care | 2025 |
| Michael Thomas Building & Roofing Ltd | Construction | 2024 |
| Michael White Snooker Ltd | Arts & recreation | 2009 |
| MID Autumn Limited | Hospitality | 2025 |
| Mikes Motors Limited | Wholesale & retail | 2011 |
| Millenium Rail 2012 Limited | Manufacturing | 2012 |
| Miller Home Care Ltd | Health & social care | 2021 |
| Mineral Extraction and Handling Limited | Mining & quarrying | 1996 |
| Minerva Medical Writing Limited | Administrative & support | 2008 |
| Minshull Enterprise Limited | Information & communication | 2024 |
| Mirdad Ltd | Other services | 2013 |
| Mirza Barbers Ltd | Other services | 2023 |
| Miss Lisa Marie Davies Consultancy Limited | Education | 2022 |
| Mixwix Gifts Limited | Wholesale & retail | 2023 |
| MJ 11 Limited | Real estate | 2006 |
| MJL South Wales Limited | Real estate | 2025 |
| MLH Holdings Ltd | Construction | 2019 |
| MLM Eco Ltd | Administrative & support | 2024 |
| MMI Trading With Care Ltd | Education | 2018 |
| Mnatsai Ltd | Administrative & support | 2022 |
| Moderncare (Neath) Ltd | Administrative & support | 2025 |
| Modu-Lite Build Limited | Construction | 2025 |
| Modu-Lite Consultancy Limited | Professional & scientific | 2024 |
| Modu-Lite Data Limited | Construction | 2025 |
| Modu-Lite Group Limited | Financial services | 2025 |
| Modu-Lite Land Limited | Real estate | 2025 |
| Modular Building Structure Group Ltd | Construction | 2026 |
| Modusx Ltd | Information & communication | 2026 |
| Mollihol Limited | Construction | 2025 |
| Monkstone Cruising & Sailing Club Ltd | Arts & recreation | 2023 |
| Monster Heating Limited | Construction | 2020 |
| Moorlands Waunarlwydd Limited | Health & social care | 2023 |
| Morgan and Williams Property Ltd | Households | 2026 |
| Morgan David Financial Services Limited | Financial services | 2018 |
| Morgan Harddie Properties Limited | Households | 2025 |
| Morgan Project Management Limited | Professional & scientific | 2022 |
| Morlich Management Limited | Professional & scientific | 2012 |
| Morris Surveying Services Ltd | Professional & scientific | 2025 |
| Morriston Car Sales Limited | Wholesale & retail | 2025 |
| Mortgages by Lynsey Ltd | Financial services | 2024 |
| Mortgages by Mark Limited | Financial services | 2025 |
| Mostyn Engineering Limited | Professional & scientific | 2024 |
| Mountain and River Activities Ltd | Arts & recreation | 2009 |
| Movai Fit Limited | Information & communication | 2026 |
| Moziva Ltd | Professional & scientific | 2026 |
| MP Roofing & Property Maintenance Ltd | Construction | 2025 |
| MR Fixit Roofing and Property Maintenance Ltd | Construction | 2025 |
| MRS T'S Woodland Wonders Ltd | Education | 2024 |
| MSC Engineering Ltd | Professional & scientific | 2019 |
| Mtaz Productions Ltd | Arts & recreation | 2022 |