| Monmouthshire Fine Wine Company Limited | Wholesale & retail | 2011 |
| Monmouthshire Housing Limited | Real estate | 2025 |
| Monmouthshire Ltd | Hospitality | 2015 |
| Monmouthshire Market Catering Limited | Hospitality | 2018 |
| Monmouthshire Motorhome Hire Ltd | Hospitality | 2022 |
| Monmouthshire Restaurants Limited | Hospitality | 2011 |
| Monmouthshire Scaffolding Services Ltd | Construction | 2022 |
| Monmouthshire Veterans Support Hub CIC | Agriculture & fishing | 2025 |
| Monterey Tile Limited | Manufacturing | 2009 |
| Moody Mabel Ltd | Wholesale & retail | 2016 |
| Moordale Ltd | Information & communication | 2023 |
| Moran Investments Ltd | Financial services | 2025 |
| Morgan & Horowskyj Architects LLP | | 2018 |
| Morgan Business Finance Ltd | Financial services | 2024 |
| Morgans Solicitors LLP | | 2023 |
| Motor Oils Direct Limited | Wholesale & retail | 2025 |
| Motorsite Ltd | Wholesale & retail | 2022 |
| Mount Pleasant Reporting Ltd | Health & social care | 2024 |
| MRI Whistance Limited | Construction | 2013 |
| Multi Vista Ltd | Real estate | 2025 |
| MW Financial Planning Limited | Financial services | 2015 |
| MW Plastering Limited | Construction | 2011 |
| My Finder Ltd | Construction | 2021 |
| My Property Partners Ltd | Real estate | 2024 |
| Myf's Kitchen Ltd. | Hospitality | 2021 |
| Myriad Business Ltd | Professional & scientific | 2020 |
| Mythos Group Ltd | Wholesale & retail | 2025 |
| N&S Jones Ltd | Health & social care | 2019 |
| Narrative Edge UK Ltd | Professional & scientific | 2017 |
| Natalie J Luckman Ltd | Professional & scientific | 2026 |
| Natalie Walker Wills Limited | Professional & scientific | 2008 |
| National Diversity Employment and Advisory Service Ltd | Administrative & support | 2021 |
| Nationwide Engineering Research & Development Ltd | Professional & scientific | 2024 |
| Natural CUT Limited | Other services | 2025 |
| Navmoor Limited | Professional & scientific | 2019 |
| Naya Bridge Ltd | Hospitality | 2020 |
| Neil Jones Developments Limited | Construction | 2018 |
| Neil Jones Property Ltd | Real estate | 2025 |
| Neju Limited | Hospitality | 2014 |
| NEO Recruitment Agency Ltd | Administrative & support | 2023 |
| Nest and Loaf Ltd | Hospitality | 2025 |
| New Abergavenny Sushi Ltd | Hospitality | 2019 |
| New Homes Solutions South Ltd | Real estate | 2019 |
| New House Farm Limited | Agriculture & fishing | 2024 |
| Newwave Design Ltd | Information & communication | 2007 |
| Ningaloo Design Limited | Professional & scientific | 2007 |
| NJP2 Ltd | Other services | 2018 |
| NK Consulting (Wales) Ltd | Transport & logistics | 2010 |
| NNW Properties Ltd | Households | 2020 |
| Nokomis Contracts Ltd | Construction | 2024 |
| North Circle Holdings Limited | Financial services | 2024 |
| Northern Linings Limited | Construction | 2018 |
| Northline Insights Limited | Professional & scientific | 2025 |
| Northwood Associates (London) Limited | Professional & scientific | 2012 |
| Novalux Holdings Limited | Financial services | 2017 |
| NR & CA Bailey Ltd | Wholesale & retail | 2002 |
| NR Brown Farriers Limited | Agriculture & fishing | 2013 |
| Numa Solutions Ltd | Professional & scientific | 2022 |
| Nzgc Limited | Manufacturing | 2016 |
| O Field Tree Surgery Limited | Administrative & support | 2008 |
| O M M S (Bristol) Limited | Health & social care | 2013 |
| O M M S (Southampton) Limited | Health & social care | 2013 |
| O3 Therapy Wales Ltd | Health & social care | 2023 |
| Oakbridge Property Limited | Real estate | 2017 |
| Oakpool Properties Limited | Real estate | 2019 |
| Oasis Communication Services Limited | Information & communication | 1997 |
| Ochram CYF | Agriculture & fishing | 2026 |
| Octocol Limited | Information & communication | 2019 |
| Ojhc Limited | Financial services | 2021 |
| Okoume Limited | Professional & scientific | 2026 |
| Oleatech Ltd | Professional & scientific | 2015 |
| Omnia Facilities Management Ltd | Construction | 2025 |
| OMP CX Enterprises Limited | Professional & scientific | 2005 |
| One Eyed Cat Limited | Wholesale & retail | 2006 |
| Only Law Limited | Professional & scientific | 2012 |
| Oomph Agency Services Limited | Professional & scientific | 2005 |
| OOT Creative Limited | Professional & scientific | 2005 |
| Open 2 Art Ltd | Education | 2025 |
| Opus-U 360 Limited | Education | 2011 |
| Orchard Cleaning Services Ltd | Administrative & support | 2019 |
| Orchestra Europa Limited | Arts & recreation | 2006 |
| Orlabell Limited | Other services | 2012 |
| Otrf Ltd | Information & communication | 2009 |
| Outshine Windows Limited | Manufacturing | 2003 |
| Ov.Prelude Limited | Professional & scientific | 2023 |
| Ovara Products Ltd | Wholesale & retail | 2025 |
| Overcrawl Ltd | Wholesale & retail | 2026 |
| Owen Davies Consulting Ltd | Professional & scientific | 2013 |
| P & P Pest Control Limited | Administrative & support | 2002 |
| P W Contracting Limited | Administrative & support | 2003 |
| P. Davies & Sons Limited | Transport & logistics | 1972 |
| Pais DE Gales Ltd | Wholesale & retail | 2025 |
| Pantygelli Escapes Ltd | Hospitality | 2024 |
| Parallel Universe Limited | Information & communication | 1994 |
| Parc Gwyn Limited | Agriculture & fishing | 2010 |
| Park Crescent Mangement Company Limited | Households | 2015 |
| Park One Consultancy Limited | Real estate | 2014 |
| Parrys Property (Abergavenny) Limited Liability Partnership | | 2005 |
| Parrys Rentals (Abergavenny) LLP | | 2013 |
| Parsnip Holdings Limited | Extraterritorial | 2022 |