| Lawiga Company Limited | Health & social care | 2024 |
| Laymak Ltd | Construction | 2013 |
| Laystone Construction Ltd | Construction | 2017 |
| LB Systems Electrical Ltd | Construction | 2025 |
| LCB Rail and Civil Engineering Limited | Construction | 2025 |
| Learn and Grow Community Interest Company | Administrative & support | 2011 |
| Learner Travel Limited | Administrative & support | 2020 |
| LEE Thompson Couriers Limited | Transport & logistics | 2022 |
| Legacy Construction ALL Aspects of Building Ltd | Construction | 2024 |
| Legacy International Group Limited | Administrative & support | 2016 |
| Legacy Training Services Ltd | Education | 2022 |
| Legends Sports Gear Ltd | Wholesale & retail | 2022 |
| Lehane Ryland AA Ltd | Other services | 2026 |
| Leighton Williams Associates Limited | Professional & scientific | 2011 |
| LEL Digital Ltd | Wholesale & retail | 2024 |
| Letts Refurb Limited | Construction | 2022 |
| Lewis Falkiner Properties Limited | Construction | 2016 |
| Lightning Solutions (Wales) Limited | Construction | 2013 |
| Lightning Solutions Holdings Limited | Administrative & support | 2023 |
| Lightning Solutions Limited | Construction | 2020 |
| Lightweight Roofing & Building Solutions Limited | Construction | 2019 |
| Linden Way Homes Ltd | Real estate | 2024 |
| Lingo Soar Cyfyngedig | Professional & scientific | 2019 |
| Linx Innovative Solutions Limited | Wholesale & retail | 2023 |
| Linxfs Financial Ltd | Financial services | 2020 |
| Little FOX Ltd | Wholesale & retail | 2018 |
| Little Lambs (Wales) Limited | Education | 2012 |
| Little Learners- Pantysgallog Ltd | Health & social care | 2019 |
| Little Legacy Lettings Ltd | Real estate | 2025 |
| Little Rascals Boutique Ltd | Wholesale & retail | 2024 |
| Little Rascals Playgroup | Education | 2008 |
| Live Life Chiropractic and Health Clinic Ltd | Health & social care | 2013 |
| Livmor Limited | Professional & scientific | 2026 |
| LJ Aerospace Limited | Manufacturing | 2020 |
| LJ Hubbard Ltd | Construction | 2014 |
| LJ Media Ltd | Professional & scientific | 2021 |
| LJ Paradise Real Estate Ltd | Real estate | 2022 |
| Ljim Limited | Construction | 2025 |
| LJL Real Estate Limited | Real estate | 2026 |
| LJM Party Limited | Wholesale & retail | 2023 |
| LL Powles Property Developments Ltd | Construction | 2025 |
| LLC Services Limited | Construction | 2019 |
| Lljm Limited | Households | 2025 |
| Llwyn YR EOS Inn Limited | Hospitality | 2024 |
| LN John Property Solutions Ltd | Households | 2026 |
| Loft Solutions Limited | Extraterritorial | 2024 |
| Louwis Commercial Property Developments Limited | Real estate | 2015 |
| Louwis Groundworks Limited | Construction | 2018 |
| LP Plant Specialists Limited | Construction | 2017 |
| LPR Surveying & Civil Engineering Limited | Professional & scientific | 2025 |
| LRG Properties Ltd | Construction | 2022 |
| LRM Maintenance and Construction Limited | Construction | 2019 |
| LUC (UK) Limited | Manufacturing | 2006 |
| Luke Dummett Bricklaying Ltd | Construction | 2016 |
| Luminous Lighting Solutions Ltd | Wholesale & retail | 2025 |
| Lunah Tearooms Limited | Hospitality | 2016 |
| LUX Nails Merthyr Ltd | Other services | 2025 |
| Luxury Retail Services Ltd | Wholesale & retail | 2024 |
| LW Housing Refurbishments Ltd | Construction | 2018 |
| Lwku Property Ltd | Real estate | 2025 |
| Lyne Collections Ltd | Wholesale & retail | 2026 |
| M & J Screening & Crushing Ltd | Water & waste | 2021 |
| M & R Valeting Ltd | Administrative & support | 2024 |
| M & S Roller Shutter Doors Limited | Construction | 2008 |
| M B T Consultancy & Training Limited | Financial services | 2014 |
| M Higgins Services Limited | Construction | 2019 |
| M Hodges Services Ltd | Construction | 2016 |
| M M Screeding Ltd | Construction | 2012 |
| M W Barry Limited | Construction | 2026 |
| M&K Wholesale Ltd | Wholesale & retail | 2025 |
| M&M Heating & Plumbing Services Ltd. | Energy | 2015 |
| M&T Heating and Plumbing Ltd | Construction | 2025 |
| M.D. Body Repairs Limited | Wholesale & retail | 2016 |
| M.E.R.S. Holdings Limited | Construction | 2022 |
| M.R.S Electrical Services Ltd | Construction | 2023 |
| MAD Developments and Construction Ltd | Construction | 2026 |
| Maggie Aquino Company Limited | Health & social care | 2022 |
| Magical Moment Events Ltd | Administrative & support | 2022 |
| Maids to Help Domestic Cleaning Ltd | Administrative & support | 2023 |
| Main Property Investments Ltd | Real estate | 2016 |
| Maintenance Matters Merthyr Ltd | Construction | 2026 |
| Mali Construction (South Wales) Ltd | Manufacturing | 2022 |
| Manorau Properties & Maintenance Ltd | Construction | 2024 |
| Maple Leaf Design & Build Ltd | Construction | 2026 |
| Marcus Alexander Estates Ltd | Administrative & support | 2019 |
| Marie Foyster Limited | Professional & scientific | 2019 |
| Mario Trucker Ltd | Transport & logistics | 2016 |
| Mariusz Bieniek Trucker Ltd | Transport & logistics | 2016 |
| Markeb Limited | Hospitality | 2024 |
| Marshal Motors Center Limited | Wholesale & retail | 2026 |
| Marshmx Holdings Limited | Financial services | 2014 |
| Marshmx Limited | Wholesale & retail | 2011 |
| Marshmx Properties Limited | Extraterritorial | 2014 |
| Martin's Framing & Galery Limited | Wholesale & retail | 2009 |
| Martyrio Ltd | Wholesale & retail | 2022 |
| Martyrs Community Club Ltd | Hospitality | 2023 |
| Masbon Limited | Professional & scientific | 2026 |
| Masleycom Properties Limited | Real estate | 2025 |
| Master Key Property Ltd | Real estate | 2022 |
| Master Key Rentals Limited | Real estate | 2026 |