| LHS Developments (South Wales) Limited | Real estate | 2018 |
| Limes Court Limited | Households | 2002 |
| Litesteps Ltd | Professional & scientific | 2024 |
| Little India @ Ltd | Hospitality | 2017 |
| Little West (Nature and Therapy) CIC | Health & social care | 2024 |
| LJS Investments Limited | Construction | 2024 |
| Llandow Metals Limited | Wholesale & retail | 2015 |
| Llandow Tuning Ltd | Wholesale & retail | 2021 |
| Llansannor House Holdings Limited | Financial services | 2009 |
| Llansannor Management Consultants Ltd | Professional & scientific | 2012 |
| Llanscapes UK Limited | Administrative & support | 2014 |
| Locke Property Investments Limited | Real estate | 2013 |
| Logsmart Limited | Manufacturing | 2020 |
| Longacre PIG and Poultry Co. Limited | Real estate | 1958 |
| Lugi Design Ltd | Professional & scientific | 2020 |
| Luna Medical Group Ltd | Other services | 2022 |
| LVL Properties Limited | Professional & scientific | 1999 |
| Lynton Court Properties LLP | | 2012 |
| M & I Howells Limited | Construction | 2016 |
| M Parts Limited | Wholesale & retail | 2003 |
| M.J. Sullivan Plasterers Ltd | Construction | 2006 |
| Macey Owen Limited | Professional & scientific | 2008 |
| Madanville Limited | Information & communication | 2010 |
| Made Fine & Co Limited | Wholesale & retail | 2017 |
| Magnet & Steel Ltd | Manufacturing | 2006 |
| Maintenance Matters (Bristol) Limited | Other services | 2008 |
| Makemson & Company Limited | Financial services | 2002 |
| Mallows Bottling Limited | Manufacturing | 2021 |
| Maple & Bean Ltd | Hospitality | 2021 |
| Marcross Cars Limited | Wholesale & retail | 2024 |
| Mark Godwin Bricklaying Contractors Limited | Construction | 2002 |
| Marley & Cory Ltd | Other services | 2023 |
| Marley's Barbers Ltd | Other services | 2024 |
| Martyn Thomas & Co. Limited | Agriculture & fishing | 1987 |
| Massie Media Ltd | Information & communication | 2025 |
| Matthew David Property Services Ltd | Construction | 2023 |
| Mazotta Limited | Agriculture & fishing | 2020 |
| Mcnamee Ethics Consulting Limited | Professional & scientific | 2025 |
| Media Industry Limited | Professional & scientific | 2018 |
| Meducan Limited | Manufacturing | 2019 |
| Meek Holdings Limited | Extraterritorial | 2016 |
| Meisgyn Case Management Limited | Health & social care | 2026 |
| Melin Holdings Limited | Professional & scientific | 2002 |
| Merthyr Property Limited | Households | 2026 |
| Metal Polishing Services Limited | Manufacturing | 2009 |
| Metrafare Limited | Real estate | 1981 |
| Mezzo Icon Properties Ltd | Real estate | 2021 |
| MGP Racing Limited | Arts & recreation | 2025 |
| Mhjg Properties Ltd | Real estate | 2021 |
| Michael Arcos & Partners Limited | Financial services | 1964 |
| Michelle Jones T/A the Red Lion Bonvilston Limited | Hospitality | 2024 |
| Midas Developments (SW) Ltd | Real estate | 2018 |
| Mike Dennison Media Ltd | Information & communication | 2014 |
| Mike Glover Consulting Limited | Professional & scientific | 2014 |
| Millfield Four Limited | Households | 2023 |
| Mimm Organics Ltd | Wholesale & retail | 2018 |
| Minnie MAY Closet Ltd | Wholesale & retail | 2021 |
| Mjl(Cardiff) Limited | Professional & scientific | 2015 |
| Mnacj Ltd | Households | 2024 |
| Mobil Build Holdings Limited | Construction | 2015 |
| Modern Celtics Ltd | Extraterritorial | 2020 |
| Monitor My Media Ltd | Wholesale & retail | 2009 |
| Moondance Foundation | Financial services | 2010 |
| Morgan Plastering and DRY Lining Limited | Construction | 1997 |
| Morgannwg CYF | Professional & scientific | 2017 |
| MPP (Cardiff) Limited | Wholesale & retail | 2021 |
| MRA Accountancy Ltd | Professional & scientific | 2023 |
| MRJ Properties Limited | Construction | 2005 |
| MSE Plant and Landscaping Ltd | Administrative & support | 2021 |
| MTA Taxis Limited | Transport & logistics | 2024 |
| Mucca Ltd | Hospitality | 2025 |
| Mughal Emperor Limited | Hospitality | 1995 |
| Mulberry Vale Trust Planning Ltd | Professional & scientific | 2013 |
| Mulcahy Creative Limited | Arts & recreation | 2017 |
| Muxcast 6 Ltd | Information & communication | 2024 |
| Muxcast 9 Ltd | Information & communication | 2024 |
| Muxcast One Limited | Information & communication | 2020 |
| Muxco Cumbria Limited | Information & communication | 2019 |
| Muxco North Wales Limited | Information & communication | 2007 |
| Muxco Wales Ltd | Information & communication | 2006 |
| MX Properties Limited | Real estate | 2013 |
| My Stiwdio Limited | Professional & scientific | 2024 |
| MYA Commercial Property Ltd | Real estate | 2022 |
| N Massie Psychology Ltd | Health & social care | 2022 |
| Nailzinc Limited | Other services | 2022 |
| Nalerick Limited | Professional & scientific | 1997 |
| Nation Broadcasting Investments (East) Ltd | Information & communication | 2018 |
| Nation Broadcasting Investments (South) Ltd | Information & communication | 2018 |
| Nation Broadcasting Investments (West) Ltd | Information & communication | 2024 |
| Nation Broadcasting Investments Limited | Information & communication | 2018 |
| Nation Broadcasting Limited | Information & communication | 1999 |
| Nation Digital Limited | Information & communication | 2016 |
| Nation Media Holdings Ltd | Information & communication | 2021 |
| Nation Media Limited | Information & communication | 2022 |
| Nation Radio Investments Limited | Information & communication | 2018 |
| Nation Radio Limited | Information & communication | 2000 |
| Nation Resources Limited | Information & communication | 2011 |
| Nation Ventures Limited | Financial services | 2020 |
| National Accident Repair Centre Ltd | Wholesale & retail | 2021 |
| Natural State Clothing Limited | Wholesale & retail | 2024 |