| Landpoint Developments Ltd | Construction | 2023 |
| Lands Property Ltd | Real estate | 2026 |
| Lang West Limited | Real estate | 2024 |
| Larkfield House Limited | Households | 2017 |
| Laserquest Limited | Wholesale & retail | 1993 |
| Lauren Ellis Creative Limited | Professional & scientific | 2024 |
| Lawrence & Company (Heating) Limited | | 1985 |
| Legal & Financial Consultants Limited | Professional & scientific | 2013 |
| Leonardo Cuisine Ltd | Hospitality | 2026 |
| LEX (Chepstow) Limited | Professional & scientific | 2014 |
| LFJ Consultancy Ltd | Professional & scientific | 2025 |
| LG Plumbing & Heating Services Ltd | Construction | 2021 |
| Liddell + Associates Limited | Professional & scientific | 2009 |
| Liliad Limited | Administrative & support | 2017 |
| Lilly Facilities Management Ltd | Administrative & support | 2015 |
| Linear Communications Consultants Ltd | Professional & scientific | 2006 |
| Lineat Composites Limited | Professional & scientific | 2020 |
| Lion Turkish Style Hair Salon Ltd | Other services | 2023 |
| Little Hoots Childminding Ltd | Health & social care | 2021 |
| Little Legends Play Ltd | Arts & recreation | 2026 |
| Little Penarth Farm Limited | Agriculture & fishing | 2004 |
| LJC Aesthetics Limited | Health & social care | 2019 |
| Llanfihangel Tor-Y-Mynydd Community Projects Limited | Other services | 2001 |
| Llanharan Limited | Professional & scientific | 2021 |
| Llanharan Properties Limited | Construction | 2024 |
| Llanharan Property Co. Limited | Construction | 2010 |
| Lockhart Network Consultancy Ltd | Information & communication | 2020 |
| LOS Kaos Limited | Arts & recreation | 2000 |
| Lower House Farm Group Ltd | Wholesale & retail | 2023 |
| Lower House Sheep Ltd | Agriculture & fishing | 2025 |
| LS Skincare Limited | Other services | 2021 |
| Luca Garden and Landscaping Ltd | Construction | 2022 |
| Lucidblue Consulting Limited | Information & communication | 2019 |
| Luff Supplies Limited | Administrative & support | 2022 |
| LUK 4 Transport Ltd | Transport & logistics | 2013 |
| Luke Aqui Mortgage Services Ltd | Financial services | 2021 |
| Lumina Dental Limited | Information & communication | 2024 |
| Luxmedtravel Ltd | Administrative & support | 2025 |
| Lydney Containers Limited | Construction | 2009 |
| Lynnant Ltd | Professional & scientific | 2018 |
| M & G Plant and Tool Ltd | Administrative & support | 2014 |
| M & G Tool Hire Ltd. | Extraterritorial | 1998 |
| M & S Lenza Ltd | Households | 2018 |
| M Hitchmough Properties Limited | Real estate | 2025 |
| M Recruit Limited | Administrative & support | 2015 |
| M&T Vaideanu Limited | Other services | 2023 |
| M.C.F.G. Cleaning Ltd | Administrative & support | 2020 |
| Macario Lewin Limited | Professional & scientific | 2006 |
| Macauley Owen Ltd | Arts & recreation | 2021 |
| Manor Carpets (Chepstow) Ltd | Wholesale & retail | 2007 |
| Marco 2020 Ltd | Transport & logistics | 2019 |
| Mario MBD Ltd | Transport & logistics | 2015 |
| Mark IT Secure Limited | Information & communication | 2017 |
| Markerson Investments Ltd | Financial services | 2020 |
| Markitup Group Ltd | Information & communication | 2026 |
| Marlow Vets Limited | Professional & scientific | 2013 |
| Marmalade House Cafe and Tea Rooms Limited | Hospitality | 2024 |
| Mathern Day Nursery (Childcare Services) Limited | Health & social care | 2009 |
| Mathern Holdings Limited | Financial services | 2019 |
| Maxstef Limited | Administrative & support | 2009 |
| Mayfair Associates Holdings Limited | Financial services | 2024 |
| Mayfair Associates Limited | Professional & scientific | 1983 |
| Mayodel Ltd | Wholesale & retail | 2022 |
| MC 478 Limited | Real estate | 2010 |
| Mcconnachie (Training and Coaching) Ltd | Education | 2022 |
| Mctlaw Limited | Professional & scientific | 2013 |
| Meddols Ltd | Health & social care | 2025 |
| Mediteraneo Ltd | Hospitality | 2024 |
| Meehill Enterprises Limited | Hospitality | 2010 |
| Meemz & MOO Ltd | Wholesale & retail | 2025 |
| MET Framing Solutions Ltd | Construction | 2015 |
| MET Structures Limited | Construction | 2017 |
| Metpurl Limited | Construction | 2015 |
| Metstruct Ltd | Construction | 2016 |
| Metstud Limited | Construction | 2017 |
| MG3 Consultancy Practice Limited | Administrative & support | 2001 |
| MH Logistics Consultancy Ltd | Professional & scientific | 2024 |
| Midway Electronics Ltd | Manufacturing | 2009 |
| Mikey Productions Ltd | Information & communication | 2022 |
| Mila Chepstow Store Ltd | Wholesale & retail | 2025 |
| Milano D&D Ltd | Hospitality | 2017 |
| Mile 27 Productions Limited | Administrative & support | 2019 |
| Miles Away (Holdings) Limited | Real estate | 2019 |
| Minerva Properties (SW) Limited | Extraterritorial | 2014 |
| Minico Limited | Hospitality | 2020 |
| Miss Scarlet Limited | Information & communication | 2023 |
| Misty Fjords Limited | Professional & scientific | 2013 |
| Mjad Services Limited | Transport & logistics | 2016 |
| ML Freight Logistics Limited | Transport & logistics | 2022 |
| MM (SW) Group Limited | Financial services | 2023 |
| MM (SW) Holdings Limited | Professional & scientific | 2015 |
| MM (SW) Limited | Wholesale & retail | 1996 |
| MM Hearing Limited | Wholesale & retail | 2023 |
| MM Hearing Solutions Ltd | Wholesale & retail | 2024 |
| Mmv&Expert Ltd | Construction | 2025 |
| Mode Tudor Services Limited | Transport & logistics | 2015 |
| Momentum Utility Services Limited | Professional & scientific | 2018 |
| MON Motors Limited | Wholesale & retail | 1976 |
| Monmouthshire Cottages LLP | | 2011 |
| Monmouthshire County Citizens Advice Bureau Ltd | Information & communication | 2008 |