| Let's Believe Ltd | Extraterritorial | 2023 |
| Light Effects Holdings Limited | Administrative & support | 2016 |
| LIM Perkins Healthcare Ltd | Health & social care | 2019 |
| Little Green Refills Limited | Wholesale & retail | 2020 |
| Little Park Consulting Ltd | Information & communication | 2004 |
| Little Seahorses Swimming Ltd | Education | 2025 |
| LK Prestige Motors Limited | Wholesale & retail | 2025 |
| Llanbedr Triskele Group Ltd | Health & social care | 2023 |
| Llangattock Mill Farm Limited | Professional & scientific | 2015 |
| Llangenny Land CIC | Real estate | 2023 |
| Llanover Day Nursery Ltd | Education | 2019 |
| Llanthony Priory Ltd | Hospitality | 2024 |
| Llanvetherine Properties Limited | Real estate | 2007 |
| Llanvihangel Court Ltd | Hospitality | 2018 |
| Lliw Building Supplies Limited | Wholesale & retail | 1991 |
| Lloyds Construction (Cymru) Limited | Construction | 2002 |
| Llwyn Melin Management Limited | Real estate | 2002 |
| Loncastre Properties Ltd | Real estate | 2026 |
| LOOK4LOCAL Ltd | Information & communication | 2002 |
| Lost the POT Ltd | Manufacturing | 2025 |
| Lotus Seven Club Limited | Other services | 2017 |
| Louis Bannon Coins & Medals Limited | Wholesale & retail | 2013 |
| Louri Ltd | Manufacturing | 2018 |
| Love Stonework Limited | Extraterritorial | 2017 |
| Love Zimbabwe | Health & social care | 2007 |
| Love Zimbabwe Fair Trade CIC | Wholesale & retail | 2010 |
| Lsullivan Holding Ltd | Financial services | 2022 |
| Lucille Wigs and Postiche Ltd | Information & communication | 2022 |
| Ludus Collections Limited | Manufacturing | 2022 |
| Lush House Ltd | Real estate | 2024 |
| M & C Auto Repairs Limited | Wholesale & retail | 2024 |
| M Bruton Construction Ltd | Construction | 2024 |
| M J Tanner Limited | Professional & scientific | 2013 |
| M N N Property Ltd | Hospitality | 2024 |
| M P Music Production Ltd | Information & communication | 2023 |
| M Powell Building Services Limited | Construction | 2012 |
| M T Consulting and Service Limited | Professional & scientific | 2010 |
| M V Construction Limited | Construction | 2003 |
| M.P.S. Surveying & Design Limited | Professional & scientific | 2004 |
| MAB Associates Limited | Public administration | 2015 |
| Mackley Davies Associates Limited | Professional & scientific | 2003 |
| MAD Consultancy Services Limited | Information & communication | 2007 |
| Made in Monmouthshire | Wholesale & retail | 2012 |
| Maerdy Ltd | Professional & scientific | 2021 |
| Mahadev Investment Property Ltd | Real estate | 2022 |
| Maiflour Limited | Hospitality | 2020 |
| Mainunit Limited | Construction | 1996 |
| Maisemore Investment Management Limited | Professional & scientific | 2024 |
| Manacrest Flat Management Limited | Other services | 1992 |
| Manso Limited | Professional & scientific | 2021 |
| Mark Fraser Consulting Ltd | Professional & scientific | 2023 |
| Marlog Capital Limited | Real estate | 2020 |
| Marston Farms Limited | Agriculture & fishing | 1977 |
| Martin Collis Ltd | Health & social care | 2023 |
| Martins Lodge Management Company Ltd | Households | 2023 |
| Masons Surveys Ltd | Construction | 2025 |
| Matei Link Ltd | Transport & logistics | 2013 |
| Matikon Trim Ltd | Manufacturing | 1992 |
| Matra Enterprises Limited | Construction | 2016 |
| Matthew Pomfret Ltd | Manufacturing | 2025 |
| Maxis Partners Limited | Professional & scientific | 2016 |
| Mayfield Livestock Limited | Wholesale & retail | 2003 |
| Mclaren Hill Ltd | Wholesale & retail | 2019 |
| Mdeh Holdings Ltd | Real estate | 2025 |
| Meadowbank Day Nursery Limited | Health & social care | 2016 |
| Medical, Scientific and Toxicology Consultancy Limited | Health & social care | 2016 |
| Melstrike Limited | Hospitality | 1989 |
| Mendoza Properties Ltd | Real estate | 2023 |
| Merlins Court Mews the Norton Tenby Management Company Limited | Real estate | 2023 |
| Merrion Farms Limited | Professional & scientific | 2006 |
| Mezo Hospitality Limited | Hospitality | 2018 |
| Mezze ME UK Ltd | Hospitality | 2018 |
| Michael Hall Photography Limited | Professional & scientific | 2009 |
| Michael Page Consulting Limited | Information & communication | 2018 |
| Michelle Smith Limited | Professional & scientific | 2013 |
| MID Wales Engineering Limited | Professional & scientific | 2000 |
| Midnight Sky Limited | Real estate | 2025 |
| Mill Estates Limited | Real estate | 2007 |
| Mill Holdings (Abergavenny) Limited | Financial services | 2022 |
| Milled + Malted Ltd | Professional & scientific | 2024 |
| Miller Research (UK) Employee Ownership Trustee Ltd | Professional & scientific | 2023 |
| Mini Digital Limited | Information & communication | 2017 |
| Miracle Workers (CC) Limited | Administrative & support | 2014 |
| Miracle Workers Agency Limited | Other services | 2003 |
| Mirage Plumbing Supplies Limited | Construction | 2009 |
| Mirai VDC Limited | Construction | 2026 |
| MJ Collective Ltd | Professional & scientific | 2020 |
| MJ Health & Fitness Ltd | Health & social care | 2021 |
| MJ Investment Holdings Ltd | Financial services | 2022 |
| MLA Engineering Ltd | Professional & scientific | 2018 |
| MMC 2100 Limited | Administrative & support | 2010 |
| Mobile Accessories Ltd | Wholesale & retail | 2014 |
| Mohaven Ltd | Hospitality | 2017 |
| Moma Cellar Limited | Manufacturing | 2022 |
| MON & Brec Tree Services Ltd | Agriculture & fishing | 2025 |
| Monahawk Developments Limited | Construction | 2012 |
| Monmouth Sushi Ltd | Hospitality | 2023 |
| Monmouthshire Bakery Limited | Manufacturing | 2011 |
| Monmouthshire Developments Limited | Real estate | 2005 |
| Monmouthshire Farming Supplies Limited | Extraterritorial | 1935 |