| Morgan and Mutch Limited | Construction | 2021 |
| Morgan Brickwork Ltd | Professional & scientific | 2015 |
| Morgan Haley Developments Ltd | Extraterritorial | 2022 |
| Morgan Precast Limited | Construction | 2017 |
| Morris & Russell Ltd | Administrative & support | 2017 |
| Morris Access Renewables Ltd | Manufacturing | 2024 |
| Morris Care Holdings Limited | Financial services | 2025 |
| Mountain Roads Ltd | Professional & scientific | 2012 |
| Mpfs Wealth Management Limited | Financial services | 2020 |
| MR BS Enterprises Ltd | Hospitality | 2024 |
| MR B’S Vape Ltd | Wholesale & retail | 2020 |
| MRG Plant Hire Limited | Construction | 2017 |
| MSJ Fabrications Limited | Manufacturing | 2006 |
| Msurvey Ltd | Construction | 2017 |
| MTC Collectables Ltd | Wholesale & retail | 2026 |
| Multi Heat Solutions Ltd | Construction | 2019 |
| Multi-Print | | 1995 |
| Munchbyte Holdings Ltd | Financial services | 2026 |
| Munchverse Ltd | Hospitality | 2025 |
| Murphy & Morgan Properties Ltd | Real estate | 2025 |
| Murphy Properties Ltd | Real estate | 2019 |
| Murray Street Dental Practice Limited | Health & social care | 2009 |
| Music Box Limited | Information & communication | 1986 |
| Music Headquarters Ltd | Administrative & support | 2018 |
| Mwrwg Logistics Ltd | Professional & scientific | 2023 |
| Mwrwg Properties Limited | Real estate | 2002 |
| My Coffee GUY Limited | Hospitality | 2023 |
| Mynydd Mawr Equestrian C.I.C. | Arts & recreation | 2024 |
| Myrtle Hill Ltd | Hospitality | 2017 |
| Myrtle House Ltd | Education | 2004 |
| N & D Building Contractors Limited | Construction | 2019 |
| N Darby Flooring Contractors Ltd | Construction | 2019 |
| N K Evans Limited | Construction | 2008 |
| N P Davies and Co Ltd | Financial services | 2022 |
| N&L Lifestyle Express Ltd | Wholesale & retail | 2020 |
| N. Waters & Sons Ltd | Construction | 2005 |
| Nadyr Washing Limited | Other services | 2025 |
| Nalinter Nchetamchi Akanchawa UK Ltd | Transport & logistics | 2020 |
| Nathos UK Limited | Wholesale & retail | 2023 |
| Nations Trust | Other services | 1998 |
| Natural Ground Care Ltd | Administrative & support | 2018 |
| NBA Developments Limited | Construction | 2004 |
| Neironft Ltd | Professional & scientific | 2026 |
| Nerys Henry CYF. | Professional & scientific | 2021 |
| Nesta Homes Ltd | Real estate | 2019 |
| Netcoder Ltd | Information & communication | 2014 |
| Neuadd Fach Ltd | Health & social care | 2007 |
| Neuro-Leading Ltd | Professional & scientific | 2024 |
| New Dock Electrical Services Ltd | Construction | 2026 |
| New Dynant Limited | Real estate | 2003 |
| New Sun Moon 888 Ltd | Hospitality | 2026 |
| New Vehicles Direct Limited | Wholesale & retail | 2016 |
| Neweuropeanstaff.Com Limited | Administrative & support | 2005 |
| Newgistics Freight Solutions Ltd | Transport & logistics | 2008 |
| Nextgeneco Limited | Information & communication | 2024 |
| Nexus Procurement Solutions Limited | Professional & scientific | 2024 |
| Nicola Angharad Jones Limited | Real estate | 2018 |
| NIK the Greek @ NO 9 Limited | Hospitality | 2018 |
| Nine Lets Limited | Arts & recreation | 2016 |
| NJ Professional Practice Solutions Ltd | Health & social care | 2026 |
| Noax Properties Ltd | Real estate | 2026 |
| Noble Family Contracts Ltd | Households | 2015 |
| Norcross FOX Limited | Real estate | 2013 |
| Nordvita Recovery Limited | Health & social care | 2025 |
| Norris Engineering Consultancy Ltd | Professional & scientific | 2022 |
| Norris Engineering Designs Ltd | Professional & scientific | 2018 |
| North Dock Valeting Limited | Administrative & support | 2024 |
| Northman Tackle Innovations Ltd | Wholesale & retail | 2025 |
| Nova Beauty and Foot Care Ltd | Health & social care | 2025 |
| Novapm Ltd | Professional & scientific | 2026 |
| Noviodunum Dunaris Limited | Hospitality | 2023 |
| NOX Recovery Ltd | Wholesale & retail | 2026 |
| Nu-Gen Renewables Limited | Construction | 2023 |
| Nu-Look Builders Limited | Construction | 1997 |
| Nubula Services Ltd | Transport & logistics | 2016 |
| Nudge Media Ltd | Information & communication | 2024 |
| Nuke Fitness Personal Training Limited | Arts & recreation | 2021 |
| Nuskool Entertainment Ltd | Administrative & support | 2020 |
| O.G. Harries Limited | Other services | 2014 |
| Oblica Consultants Limited | Professional & scientific | 2001 |
| Oderzo Ltd | Hospitality | 2024 |
| OGN Limited | Hospitality | 2003 |
| OH LA Lash and Beauty Ltd | Other services | 2024 |
| Oliver Jordan Transport Ltd | Transport & logistics | 2019 |
| Olivinia Limited | Wholesale & retail | 2023 |
| Olympic Upvc Products Limited | Manufacturing | 1990 |
| OMJ2ITCONSULTING Ltd | Information & communication | 2021 |
| One of a Kind Ceramics Ltd | Manufacturing | 2022 |
| Onesta Clothing Ltd | Wholesale & retail | 2020 |
| Online Legal Services Solicitors Limited | Professional & scientific | 2016 |
| Opes Housing Limited | Real estate | 2024 |
| Opex LAB Ltd | Professional & scientific | 2025 |
| Optical Power Limited | Manufacturing | 2013 |
| Optimwm Ltd. | Information & communication | 2014 |
| Opulence Bar Group Ltd | Hospitality | 2022 |
| Orgone Fusion Creations Ltd | Wholesale & retail | 2025 |
| Oris Swansea Limited | Health & social care | 2011 |
| ORS (HD) Limited | Administrative & support | 2018 |
| ORS Contract Management Limited | Real estate | 1989 |
| Orthodonteg CYF | Real estate | 2007 |