| M&D Rentals Limited | Real estate | 2021 |
| M&E Coaching Limited | Wholesale & retail | 2022 |
| M&E Glow Ltd | Wholesale & retail | 2025 |
| M&N Davies Car Sales Limited | Wholesale & retail | 2012 |
| M'Eating Point Ltd | Hospitality | 2017 |
| M.F.D. Capacitors (1991) Limited | Manufacturing | 1991 |
| M.K Driver Ltd | Transport & logistics | 2017 |
| M.M. Surveying Services Ltd | Professional & scientific | 2007 |
| M.W. Civil Engineering Ltd | Construction | 2007 |
| M1 Nails Wrexham Ltd | Other services | 2024 |
| M19LOGISTICS Limited | Transport & logistics | 2019 |
| MA Fitting Solutions Limited | Wholesale & retail | 2016 |
| MA Holdco Ltd | Financial services | 2024 |
| MA Imrie Consultancy Ltd | Professional & scientific | 2021 |
| Maahis Wrexham Ltd | Hospitality | 2019 |
| Maas Spectrometry Ltd | Manufacturing | 2020 |
| Maccas Munch Ltd | Hospitality | 2025 |
| Maccs Group Ltd | Professional & scientific | 2018 |
| Machina Education Ltd | Information & communication | 2026 |
| Machine House Limited | Hospitality | 1981 |
| Maciej Janczewski Transport Ltd. | Transport & logistics | 2017 |
| Macintosh Holdings Ltd | Financial services | 2023 |
| Maciver & Medinger Ltd | Real estate | 2025 |
| Mack Salon (I) Limited | Other services | 2003 |
| Mack Salon (II) Limited | Other services | 2007 |
| Macs Supplies Ltd | Construction | 2020 |
| Macsteve Solutions Ltd | Information & communication | 2025 |
| Made UP (Chirk) Limited | Other services | 2022 |
| Madison Oaks Limited | Construction | 2017 |
| Madog Roller Doors Limited | Construction | 2021 |
| Maelor Construction 2019 Limited | Construction | 2019 |
| Maelor Engineering Limited | Manufacturing | 2006 |
| Maelor Farm and Garden Limited | Wholesale & retail | 2009 |
| Maelor Food Solutions Limited | Professional & scientific | 2022 |
| Maelor Investments Ltd | Financial services | 2026 |
| Maes Glan 18 7 1971 Limited | Extraterritorial | 2013 |
| Maes Y Pant/Hollowfield Action Group Limited | Other services | 2007 |
| Maesgwyn Estate Limited | Real estate | 1987 |
| Magellan Aerospace (UK) Limited | Manufacturing | 2003 |
| Maggie’S Cafe (Holt) Limited | Wholesale & retail | 2021 |
| Magnark Ltd | Real estate | 2026 |
| Magnex Exercise Technology Limited | Manufacturing | 2013 |
| Magno Holdings Limited | Financial services | 2017 |
| Magno Limited | Manufacturing | 2011 |
| Magno Properties Limited | Real estate | 2017 |
| Magnolia House Residential Home Limited | Health & social care | 2014 |
| Magnum Engineering Ltd | Professional & scientific | 2022 |
| Magog Ltd | Wholesale & retail | 2026 |
| Magyar Cymru CIC | Education | 2023 |
| Maidstone Theatre School LLP | | 2025 |
| Majestic Roofing Contractors Ltd | Construction | 2025 |
| Major Modz Joinery Limited | Construction | 2025 |
| MAK Smile Ltd | Health & social care | 2026 |
| Makes Homes Ltd | Real estate | 2024 |
| Malcolm Davies & Sons Developments Limited | Construction | 2008 |
| Malcolm Randles Aerial & Satellite Services Ltd | Information & communication | 2013 |
| Mallu's Kitchen Ltd | Hospitality | 2025 |
| Malone’S Construction Limited | Construction | 2024 |
| Malpas Vintage Machinery Association Limited | Other services | 1982 |
| MAN Logistics Group Ltd | Transport & logistics | 2026 |
| Management Succession (Wales) Limited Partnership | | 2018 |
| Management Succession GP Limited | Financial services | 2017 |
| Mandjulee Holdings Limited | Real estate | 2010 |
| Mangroove Entertainment Ltd | Hospitality | 2025 |
| Manifestwithclaire Ltd | Administrative & support | 2024 |
| Manliv Limited | Real estate | 2016 |
| Manorspace Ltd | Real estate | 2014 |
| Manutech Europe Limited | Manufacturing | 1986 |
| Many Hands Productions Limited | Information & communication | 2007 |
| MAP Developments (NW) Limited | Construction | 2012 |
| Maple & Stone Limited | Manufacturing | 2019 |
| Maple Green Developments Limited | Hospitality | 2008 |
| Maple Green Fine Foods Limited | Manufacturing | 2020 |
| MAR Shop Ltd | Administrative & support | 2016 |
| Marcher Storage Systems Limited | Construction | 2003 |
| Marchwiel Hall Events Limited | Hospitality | 2014 |
| Marcle Leisure Ltd | Wholesale & retail | 2019 |
| Marcus Wright Salons Limited | Other services | 2018 |
| Marford Construction Limited | Construction | 2017 |
| Marford Engineering Ltd | Professional & scientific | 2019 |
| Marford Limited | Professional & scientific | 2015 |
| Marford Playgroup Little Explorers Ltd | Health & social care | 2019 |
| Mark & Orion UK Limited | Manufacturing | 2015 |
| Mark Home Improvements Limited | Administrative & support | 2019 |
| Mark Jones Plumbing & Heating (NW) Ltd | Construction | 2017 |
| Mark Murray Contracting Ltd | Transport & logistics | 2012 |
| Mark Specialist Applications Limited | Manufacturing | 2011 |
| Market Movers Official Limited | Professional & scientific | 2026 |
| Marketing Data Solutions Ltd | Information & communication | 2009 |
| Marketing Million Ltd | Professional & scientific | 2019 |
| Markos Properties (Whitchurch) Ltd | Real estate | 2023 |
| Markos Properties Ltd | Real estate | 2020 |
| Marles Homes Limited | Real estate | 2021 |
| Marley Grove Management Committee Limited | Households | 2017 |
| Marley's Magical Creations Ltd | Arts & recreation | 2022 |
| Marleys Rentals Ltd | Real estate | 2023 |
| Marlin Industries Holdings Limited | Financial services | 2025 |
| Marlin Industries Limited | Professional & scientific | 1998 |
| Marling Limited | Hospitality | 2003 |
| Marlizia Ltd | Health & social care | 2020 |