| Lewis Hughes Drums Ltd | Education | 2023 |
| Lewis Motors (Merthyr) Limited | Wholesale & retail | 2011 |
| Lewis Sun Limited | Hospitality | 2021 |
| LGS Llwydcoed Limited | Hospitality | 2026 |
| LH ISW Services Ltd | Health & social care | 2024 |
| License to Grill SW Ltd | Wholesale & retail | 2025 |
| Lighthouse of GOD Ministries (Logm) | Education | 2004 |
| Lightning Brothers Ltd | Hospitality | 2019 |
| Lincai (Trading) Limited | Hospitality | 2018 |
| Lincai Limited | Real estate | 2017 |
| Lindogs Ltd | Wholesale & retail | 2024 |
| Linklight Network Solutions Limited | Information & communication | 2025 |
| Linline Limited | Construction | 2021 |
| Little Lamb Media Ltd | Information & communication | 2025 |
| Little-Fox Pictures Ltd | Information & communication | 2025 |
| LJ Motorsport Ltd | Other services | 2024 |
| LJB Maintenance Services Ltd | Manufacturing | 2024 |
| LKR Consultancy Ltd | Information & communication | 2024 |
| Llettyshenkin Construction Company Limited | Construction | 2001 |
| Llewellyn Tree Services Limited | Agriculture & fishing | 2015 |
| Lloyd Jones Complete Flooring Ltd | Construction | 2026 |
| Lloyd Walters Industrial Services Limited | Administrative & support | 2017 |
| Load-Lok Manufacturing Limited | Manufacturing | 1991 |
| Load-Lok UK Ltd | Wholesale & retail | 1998 |
| LOC Security Ltd | Construction | 2020 |
| Lodge Living Limited | Hospitality | 2021 |
| Loft Pro Cardiff Ltd | Construction | 2014 |
| Longmeadow Partnership Ltd | Construction | 2003 |
| Looking Good MCS Limited | Other services | 2013 |
| LOW FEE Claims Ltd | Professional & scientific | 2019 |
| LOWERPRICE4U Ltd | Wholesale & retail | 2009 |
| LP Construction & Maintenance Ltd | Construction | 2022 |
| LRD Taps Ltd | Hospitality | 2020 |
| LTN 888 Limited | Real estate | 2018 |
| LTW Telecommunications Limited | Information & communication | 2016 |
| Lucas Home Solutions Ltd | Real estate | 2025 |
| Lucky Little Panda Ltd | Hospitality | 2026 |
| Luke Maddy and SON Services Ltd | Mining & quarrying | 2023 |
| Luke Williams Post Production Limited | Arts & recreation | 2016 |
| Lukerail Ltd | Construction | 2022 |
| Luvara Ltd | Wholesale & retail | 2025 |
| Luxury Home Improvements Limited | Construction | 2015 |
| Lygo Online Retailing Ltd | Wholesale & retail | 2018 |
| Lyndhurst 1964 Limited | Extraterritorial | 2014 |
| Lynx Hairdressing Ltd | Other services | 2017 |
| M & E Evans Limited | Health & social care | 2017 |
| M and B Moveable Walls Ltd | Other services | 2010 |
| M Colcombe Interiors Ltd | Construction | 2011 |
| M L Crane Services Ltd | Manufacturing | 2018 |
| M Morgan Maintenance & Building Ltd | Construction | 2021 |
| M S Davies Ltd | Professional & scientific | 2006 |
| M Williams Building & Plastering Ltd | Construction | 2025 |
| M&S Harris Ltd | Professional & scientific | 2024 |
| Macatrillion Aeronautical & Systems Engineering Ltd | Professional & scientific | 2024 |
| Maesyffynon Garage Ltd | Wholesale & retail | 2010 |
| MAK Agile Consultancy Ltd | Professional & scientific | 2026 |
| Malik Properties Aberdare Ltd | Real estate | 2015 |
| Mandrake Events Limited | Other services | 2022 |
| Manning Estate Agents Ltd | Real estate | 2013 |
| Manufacturing WS Limited | Other services | 2020 |
| Marbella White Ltd | Wholesale & retail | 2026 |
| Marek Pydo Haulage Ltd | Transport & logistics | 2018 |
| Margaret Golder Bookkeeping Services Ltd | Professional & scientific | 2011 |
| Mark Rees & Sons Limited | Construction | 2006 |
| Marpol Vehicle Leasing Limited | Extraterritorial | 2002 |
| Marpol Vehicles Limited | Extraterritorial | 2002 |
| Marstock Properties Ltd | Real estate | 2025 |
| MAS Security Solutions Ltd | Administrative & support | 2025 |
| Mathu Business Solutions Limited | Information & communication | 2016 |
| Matthewtransportservices Ltd | Transport & logistics | 2019 |
| Mattix Installations Ltd | Construction | 2025 |
| Mattix Locksmiths Ltd | Manufacturing | 2023 |
| Maxwell & Franks Limited | Manufacturing | 2021 |
| Mayfair Private Limited | Wholesale & retail | 2020 |
| MC DRV Ltd | Transport & logistics | 2024 |
| Mccoy Quality Solutions Limited | Professional & scientific | 2010 |
| Mdbg Properties Ltd | Real estate | 2024 |
| Mears Accountancy Ltd | Professional & scientific | 2005 |
| Mechurion Limited | Construction | 2005 |
| Merthyr Development Park Limited | Real estate | 2024 |
| Mesut Karakus Ltd | Administrative & support | 2018 |
| Metalrix Limited | Manufacturing | 2025 |
| Metier Professionals Occupational Health Services Ltd | Administrative & support | 2025 |
| MH Properties (Aberdare) Ltd | Real estate | 2008 |
| MHW Developments Ltd | Construction | 2021 |
| MHW Entertainments Ltd | Hospitality | 2022 |
| Michael Williams Electrical Ltd | Construction | 2026 |
| Mike Evans Building & Plastering Contractors Ltd | Construction | 2012 |
| Mike Upton Limited | Other services | 2018 |
| Mila’Scakery Limited | Wholesale & retail | 2024 |
| Millennium Motorcycles Ltd | Transport & logistics | 2004 |
| Milrock Holdings Limited | Financial services | 2021 |
| Miollu Limited | Construction | 2025 |
| MIRAC68 Property Ltd | Real estate | 2024 |
| Mirror Image #the Salon Ltd | Other services | 2015 |
| MJ Property Maintenance Services Ltd | Construction | 2025 |
| Mjac Ltd | Other services | 2020 |
| MLC Gardens Ltd | Construction | 2020 |
| Monarch Architectural Services Ltd | Professional & scientific | 2008 |
| Montgomery-Williams LLP | | 2026 |