| Lurgyroe Glen Open Space Management Company Limited | Households | 2021 |
| LÍR Pictures Limited | Information & communication | 2025 |
| M & G Carroll Ltd | Construction | 2008 |
| M & K Holdings (Ireland) Limited | Manufacturing | 2005 |
| M & K Quarry Plant Ltd | Manufacturing | 2004 |
| M Dorman & SON Ltd | Other services | 2024 |
| M G Quarry Plant Ltd | Manufacturing | 2014 |
| M Hamill Construction Ltd | Construction | 2006 |
| M Hughes Construction Ltd | Construction | 2026 |
| M P Coleman Limited | Manufacturing | 2021 |
| M R Real Estate Limited | Real estate | 2026 |
| M&E Steel Fabrications Limited | Professional & scientific | 2018 |
| M&K Auto Services Limited | Wholesale & retail | 2024 |
| M&K ENG Ltd | Manufacturing | 2016 |
| M&K Sales (Global) Ltd | Manufacturing | 2026 |
| M&L Property Developments Ltd | Construction | 2017 |
| M&M Steelfix Ltd | Manufacturing | 2013 |
| M&N Engineering Ltd | Professional & scientific | 2019 |
| M&P Hamill Limited | Construction | 2021 |
| M-Elite Leadership Ltd | Health & social care | 2026 |
| M.J. Timber Ltd | Manufacturing | 2012 |
| M.L. White Solicitors Ltd | Professional & scientific | 2012 |
| M1 Service Area Limited | Real estate | 2003 |
| MAC 4 Engineering Ltd | Manufacturing | 2020 |
| MAC Animal Health Ltd | Manufacturing | 2015 |
| MAC Cable Utilites Ltd | Construction | 2017 |
| MAC Cladding Limited | Manufacturing | 2015 |
| MAC Motors Trade Sales Ltd | Wholesale & retail | 2021 |
| MAC Zero Holdings Limited | Financial services | 2025 |
| MAC Zero Ireland Holdings Limited | Financial services | 2025 |
| MAC Zero Modular Buildings Ltd | Construction | 2020 |
| Mace Madden Ltd | Wholesale & retail | 2022 |
| Mace Middletown Ltd | Wholesale & retail | 2022 |
| Macha Media Limited | Information & communication | 2012 |
| Machine Truck Services Ltd | Wholesale & retail | 2012 |
| Mackbros Ltd | Information & communication | 2026 |
| Mackle Communications Limited | Professional & scientific | 2022 |
| Mackle Consulting Limited | Extraterritorial | 2023 |
| Mackle Dental Ltd | Health & social care | 2026 |
| Mackle Ingredients Limited | Manufacturing | 2020 |
| Mackle Snacks Limited | Manufacturing | 2005 |
| Madame Carle Limited | Energy | 2013 |
| Made of Gold Entertainment Ltd | Arts & recreation | 2013 |
| Maghermoy Limited | Hospitality | 2023 |
| Maghery District Hall Committee | Professional & scientific | 2012 |
| Maghery Property Developments Ltd | Construction | 2019 |
| Maghery Rural Enterprise Centre | Real estate | 1999 |
| Magnet Solutions (NI) Limited | Information & communication | 2006 |
| Magnoverse Ltd | Wholesale & retail | 2025 |
| Magnum Trading Limited | Wholesale & retail | 2023 |
| Magwall Limited | Construction | 2019 |
| Mainland Trading (N.I.) Limited | Transport & logistics | 2022 |
| Mainland Trading (UK) Limited | Transport & logistics | 2014 |
| Mainline Holdings (NI) Limited | Construction | 1973 |
| Mainplant Ltd | Manufacturing | 2007 |
| Maintain My Fleet Ltd | Wholesale & retail | 2026 |
| Maison JC Ltd | Wholesale & retail | 2026 |
| Majestic Property Ltd | Real estate | 2025 |
| Makau Group Limited | Financial services | 2025 |
| Mala Accountancy Services Ltd | Professional & scientific | 2024 |
| Mala Construction Limited | Construction | 2020 |
| Mala Project Management Limited | Extraterritorial | 2024 |
| Malforge Investments Limited | Extraterritorial | 1960 |
| Mallaghan (Holdings) Limited | Professional & scientific | 2006 |
| Mallaghan Airport BUS Company Limited | Manufacturing | 2017 |
| Mallaghan Parts Limited | Wholesale & retail | 2024 |
| Mallaird Limited | Wholesale & retail | 2024 |
| Mallon & Mallon Ltd | Professional & scientific | 2012 |
| Mallon Best Limited | Real estate | 2025 |
| Malplas Ltd | Manufacturing | 2000 |
| Malumera Ltd | Wholesale & retail | 2026 |
| MAM Property Ltd | Real estate | 2018 |
| Mamoru Properties Limited | Real estate | 2025 |
| Maneely & Co Limited | Real estate | 2003 |
| Manorwood Doors Ltd | Construction | 2013 |
| Mantas Bacius Ltd | Extraterritorial | 2023 |
| Marden Property Developments Limited | Construction | 2003 |
| Margaret Marks Ltd | Wholesale & retail | 2025 |
| Mark Reihill Ltd | Arts & recreation | 2018 |
| Mark Turbitt Transport Ltd | Transport & logistics | 2020 |
| Market Development (NI) Limited | Professional & scientific | 2015 |
| Martec NI Limited | Manufacturing | 2004 |
| Martin Mallon Ltd | Professional & scientific | 2013 |
| Martin Traynor Motors Limited | Wholesale & retail | 2007 |
| Martin Traynor Sales Limited | Wholesale & retail | 2024 |
| Martin's Classic Garage Ltd | Wholesale & retail | 2022 |
| Martin's Funeral Directors Ltd | Other services | 2020 |
| Martin's Service Station Ltd | Wholesale & retail | 2020 |
| Maskurader LLC Limited | Manufacturing | 2024 |
| Mass Timber Consultancy Ltd | Construction | 2023 |
| Matthew Property Ltd | Real estate | 2024 |
| Maurice Millar Ltd | Construction | 2016 |
| Maurice Stevenson Limited | Construction | 1965 |
| Maxwell (NI) Limited | Agriculture & fishing | 2013 |
| MB Financial Services Ltd | Financial services | 2019 |
| Mbrq NI Ltd | Construction | 2026 |
| MC D'S Tools Ltd | Wholesale & retail | 2018 |
| MC Fitness Ltd. | Arts & recreation | 2015 |
| MC Freight Ltd | Transport & logistics | 2022 |
| MC Ginn Mechanical Ltd | Construction | 2025 |