| Llafur Dros Annibyniaeth Ltd | Other services | 2021 |
| Lock OFF Limited | Information & communication | 2021 |
| Lougher Home Care Limited | Health & social care | 2008 |
| Louise Goulding Limited | Professional & scientific | 2009 |
| Lovell and Co (Monmouthshire) Limited | Professional & scientific | 2024 |
| LOW Profile Productions Ltd. | Information & communication | 1993 |
| Lucascristian Ltd | Wholesale & retail | 2022 |
| Luckysox Competitions Limited | Arts & recreation | 2025 |
| Lucy MAY Lifestyle Ltd | Other services | 2020 |
| LVL Walls and Floors Ltd | Construction | 2023 |
| Lyons Gate Holdings Limited | Real estate | 2020 |
| Lyons Gate Properties Limited | Real estate | 2008 |
| Mabe's Guttering Limited | Administrative & support | 2026 |
| MAC Agency Ltd | Health & social care | 2016 |
| Macomon Limited | Professional & scientific | 2019 |
| Mad-Hoc Limited | Health & social care | 2023 |
| Magor Developments Limited | Construction | 2011 |
| Magor Motors Limited | Transport & logistics | 2015 |
| Magor With Undy Sports and Leisure Association | Other services | 2009 |
| Main Source Heating Ltd | Construction | 2024 |
| Maindee Fresh Food Limited | Real estate | 1969 |
| Maison DE Darvill Limited | Wholesale & retail | 2025 |
| Making Politics Interesting Limited | Professional & scientific | 2007 |
| Malam Properties Limited | Real estate | 2016 |
| Mallard Court (School Road North) Management Company Limited | Households | 2012 |
| Mallow Estates Limited | Real estate | 2019 |
| Maltings Property Limited | Real estate | 2025 |
| Maple (140) Limited | Water & waste | 2000 |
| Mapstone Property Limited | Real estate | 2025 |
| Mark a Hopkins Limited | Construction | 2008 |
| Mark Purkis Roofing Ltd | Construction | 2025 |
| Mark's Mobile Butchers Delivery Ltd | Hospitality | 2025 |
| Mark's Mobile Butchers Limited | Wholesale & retail | 2016 |
| Marsh Horizon Limited | Professional & scientific | 2017 |
| Marshall NDT Services Ltd | Professional & scientific | 2026 |
| Martin Technical Services (South Wales) Limited | Information & communication | 1999 |
| Maryam Jewellery Limited | Wholesale & retail | 2021 |
| Masterplan Computer Aided Drawings Limited | Professional & scientific | 1997 |
| Matchbox Pickleball Ltd | Arts & recreation | 2026 |
| Materials Recovery Systems Ltd | Extraterritorial | 2020 |
| Mathematically Possible Limited | Wholesale & retail | 2016 |
| Maynard's Property Developments Ltd | Real estate | 2023 |
| Mbcf Consulting Limited | Information & communication | 2015 |
| MBE Property & Renovations Ltd | Construction | 2021 |
| Mccarthy Hunt Ltd | Real estate | 2025 |
| MCD Organisation Holdings Limited | Financial services | 2018 |
| Mcfarlane Training Limited | Education | 2022 |
| Mechserve Maintenance Services Ltd | Manufacturing | 2015 |
| Medeventures 1 Ltd | Professional & scientific | 2022 |
| Medeventures 2 Ltd | Professional & scientific | 2023 |
| Medeventures Ltd | Financial services | 2022 |
| Medhurst Property Developments Ltd | Construction | 2020 |
| Merlin Alarms Limited | Professional & scientific | 2016 |
| Mermaid Studios UK Ltd | Information & communication | 2026 |
| Mgct Enterprises Limited | Professional & scientific | 2016 |
| Micm Ltd | Professional & scientific | 2024 |
| Mike Powell Mortgages Ltd | Financial services | 2019 |
| Millies Welshcakes Ltd | Wholesale & retail | 2024 |
| Mistral Building Solutions Limited | Professional & scientific | 2004 |
| Moeseg Consulting Limited | Information & communication | 2024 |
| Monmouthshire Accommodation Limited | Real estate | 2019 |
| Monmouthshire Biomechanics Ltd | Other services | 2020 |
| Monmouthshire Driveways and Landscaping Ltd | Construction | 2023 |
| Monmouthshire Gate Company Ltd Ltd | Construction | 2019 |
| Monmouthshire Milk Ltd | Hospitality | 2021 |
| MOO Moo's Coffee Shop Limited | Hospitality | 2017 |
| Moon & Co Sales Limited | Real estate | 2017 |
| Moon & Co. (Caldicot) Limited | Real estate | 2003 |
| Movmem Ltd | Information & communication | 2024 |
| Movvix Limited | Transport & logistics | 2025 |
| MP PR Limited | Professional & scientific | 2019 |
| MR LT Limited | Information & communication | 2019 |
| MRE Davies Ltd | Real estate | 2025 |
| MSP 2018 Limited | Professional & scientific | 2018 |
| Muddy Series 4X4 Ltd | Wholesale & retail | 2021 |
| Mustoe Developments Limited | Construction | 2018 |
| Mustoes Properties Limited | Wholesale & retail | 2019 |
| Mustoes Specialist Vehicle Body Repairs Limited | Wholesale & retail | 2016 |
| Myadminmate Ltd | Information & communication | 2025 |
| N & M Groundworks Limited | Construction | 2023 |
| N-Virojet Site Services Ltd | Administrative & support | 2024 |
| Napoli Brothers Limited | Hospitality | 2018 |
| Nathan Forder Building & Groundwork Limited | Construction | 2014 |
| Natural Powered World Limited | Construction | 2014 |
| Nazado Ltd | Wholesale & retail | 2020 |
| NBR Transport Limited | Transport & logistics | 2014 |
| NC Fish Bar Ltd | Wholesale & retail | 2025 |
| NCL Consultants Limited | Administrative & support | 2025 |
| Nedern Estates Ltd | Households | 2017 |
| Neil Bussey Limited | Professional & scientific | 2022 |
| Neural Vectra Ltd | Information & communication | 2026 |
| New Asgard Limited | Health & social care | 2024 |
| New Caldicot Classic Barber Ltd | Other services | 2021 |
| New Home Investments Ltd | Construction | 2025 |
| New Works Signalling Ltd | Construction | 2013 |
| Nexus Global Recruitment Limited | Administrative & support | 2024 |
| NH Consultancy Solutions Ltd | Professional & scientific | 2023 |
| NH Controls Limited | Professional & scientific | 2016 |
| Nirvana Coffee & Wine Ltd | Hospitality | 2025 |
| Nitesh Ltd | | 2014 |