| Merchasylum Ltd | Manufacturing | 2011 |
| Meridian and Welsh Guild of Spar Limited | Administrative & support | 2008 |
| Metdem Limited | Water & waste | 2022 |
| Metdem Recycling Limited | Water & waste | 2023 |
| MF4 Solutions Limited | Professional & scientific | 2022 |
| MGF Strategies Ltd | Professional & scientific | 2024 |
| Mi:Skin Beauty Limited | Other services | 2014 |
| MIA Bella's Candles UK Limited | Wholesale & retail | 2021 |
| Millennium Personnel Services (Holdings) Limited | Administrative & support | 2012 |
| Millennium Personnel Services Limited | Administrative & support | 1998 |
| Millstone Construction & Electrical (Wales) Limited | Construction | 2003 |
| Mini Acorns Ltd | Health & social care | 2024 |
| Mint Llantrisant PLC | Manufacturing | 2005 |
| Mint Online Marketing Ltd. | Information & communication | 2004 |
| Minxies Beauty Limited | Other services | 2017 |
| Miras Consulting Ltd | Professional & scientific | 2026 |
| Miskin Glazing Ltd | Construction | 2026 |
| Miskin Pharm Limited | Wholesale & retail | 2022 |
| Miss De-Vyliers Limited | Wholesale & retail | 2017 |
| Mission Billionare Ltd | Wholesale & retail | 2025 |
| MJE Property Holdings Ltd | Real estate | 2020 |
| MJM Mortgages & Protection Ltd | Financial services | 2025 |
| MJM Wills & Estate Planning Ltd | Financial services | 2026 |
| MJS Financial Services Ltd | Professional & scientific | 2020 |
| MJS Probate & Estate Planning Limited | Professional & scientific | 2025 |
| Mlhn Limited | Arts & recreation | 2026 |
| MMB Property Development Ltd | Real estate | 2024 |
| MMB Vapourz Limited | Wholesale & retail | 2022 |
| MOB Trading Ltd | Manufacturing | 2024 |
| Modern Mobility Solutions Ltd | Wholesale & retail | 2019 |
| Money Made Calmer Limited | Education | 2026 |
| Moneywales Limited | Financial services | 2008 |
| Morgeisi Ltd | Professional & scientific | 2024 |
| Morris Property Holdings Ltd | Real estate | 2025 |
| Moss Barber Studio Ltd | Other services | 2023 |
| Mother HEN Eggs Limited | Wholesale & retail | 2024 |
| Mothers Matter C.I.C. | Health & social care | 2020 |
| Motorjoint Limited | Information & communication | 1998 |
| Moulvi Bazaar Khulna Limited | Hospitality | 2025 |
| Move and Form CYF | Health & social care | 2026 |
| Move IT Lettings & Management Limited | Real estate | 2011 |
| Move Yoga Studio CYF | Health & social care | 2024 |
| Mozzi’S Kitchen Ltd | Hospitality | 2023 |
| MPB Digital Transformation Limited | Professional & scientific | 2026 |
| MRC Carpentry & Renovations Ltd | Construction | 2025 |
| MS Splicing Services Ltd | Information & communication | 2019 |
| MSF Building Limited | Construction | 2017 |
| Msld Properties Ltd | Real estate | 2024 |
| MT2WALES Limited | Professional & scientific | 2002 |
| Multi Choice Partnership Ltd | Wholesale & retail | 2021 |
| Multi Choice Tiles Discount Warehouse Limited | Wholesale & retail | 2006 |
| MVC Specialists Limited | Information & communication | 2012 |
| MVSS01 Ltd | Administrative & support | 2020 |
| MWR Motorcycles Ltd | Wholesale & retail | 2018 |
| My Healthy Steps Ltd | Health & social care | 2021 |
| My Little Feet Limited | Wholesale & retail | 2025 |
| Mytrusteebuilder Ltd | Construction | 2021 |
| N Stokes Limited | Other services | 2016 |
| N2R Electrical Ltd | Construction | 2018 |
| Nanotto UK Limited | Real estate | 2003 |
| Natural RAW Limited | Wholesale & retail | 2020 |
| Nature Pathways CIC | Education | 2026 |
| Nautilus Concrete & Flooring Ltd | Construction | 2023 |
| Nautilus Roofing & Exteriors Ltd | Construction | 2013 |
| Neil Porter Associates Limited | Information & communication | 2001 |
| Neil Richardson Consulting Ltd | Professional & scientific | 2015 |
| Neil Smith Developments Limited | Construction | 2018 |
| Network Recruitment Wales Limited | Administrative & support | 2019 |
| Neuadd WEN Tnmp Limited | Agriculture & fishing | 2025 |
| Newtenfour Limited | Administrative & support | 1998 |
| Nexastream Ltd | Information & communication | 2024 |
| Nexdorf Electrical Control Engineering Limited | Manufacturing | 2003 |
| Ngalaphi Limited | Extraterritorial | 2016 |
| NHP Landscapes Ltd | Administrative & support | 2026 |
| Niccmotorcyles Limited | Financial services | 2023 |
| Nick Preece Comms Ltd | Administrative & support | 2020 |
| NO Limits Neurodiversity Limited | Education | 2019 |
| NO. 20 Cowbridge Road Ltd | Real estate | 2023 |
| Nocturne Voltaire Ltd | Hospitality | 2018 |
| Noden Energy Ltd | Construction | 2020 |
| NOT 2 Heavy Engineering Ltd | Professional & scientific | 2020 |
| NOW (NO Other Way) CIC | Wholesale & retail | 2020 |
| Noyb Limited | Professional & scientific | 2016 |
| NR & RM Shearman Limited | Wholesale & retail | 2008 |
| NT Holdings South Wales Ltd | Real estate | 2023 |
| Nutristore Limited | Wholesale & retail | 2025 |
| Nutrivend Vending Limited | Wholesale & retail | 2025 |
| O H Richards Limited | Information & communication | 2010 |
| O T Sparks Farming Ltd | Agriculture & fishing | 2025 |
| O&H Consulting Ltd | Professional & scientific | 2024 |
| Oasis Pools Limited | Construction | 2026 |
| Olimor Software Limited | Information & communication | 2009 |
| Omen Films Cymru CIC | Information & communication | 2025 |
| Openmaps Limited | Information & communication | 2024 |
| Optiqs on Limited | Information & communication | 2024 |
| ORB Commercial Solutions Limited | Financial services | 2013 |
| Ordo Security Services Ltd | Administrative & support | 2021 |
| Oska's Ltd | Professional & scientific | 2000 |
| Ourd Holdings Ltd | Construction | 2019 |
| Ourd Ltd | Professional & scientific | 2019 |