| Mcnally & Turner Properties Ltd | Real estate | 2021 |
| Mcneill (Properties) Limited | Real estate | 1948 |
| MD Healthcare Contracting Limited | Health & social care | 2023 |
| MD Healthcare Limited | Health & social care | 1998 |
| MD78 Ltd | Wholesale & retail | 2023 |
| Meadow House Management Company (NI) Limited | Extraterritorial | 2006 |
| Meadowfields Close Management Limited | Extraterritorial | 2007 |
| Medoll Tech Limited | Wholesale & retail | 2025 |
| Meeks Distribution Ltd | Transport & logistics | 2006 |
| Meet Star Limited | Wholesale & retail | 2024 |
| Meghna (N.I.) Limited | Hospitality | 2020 |
| Meilai Limited | Wholesale & retail | 2024 |
| Melmal Ltd | Information & communication | 2016 |
| Mengxiaoxiao Limited | Wholesale & retail | 2024 |
| Mergellus Ltd | Construction | 2024 |
| Merotshe Limited | Wholesale & retail | 2025 |
| Mescost Limited | Wholesale & retail | 2025 |
| Messrs Magill Ltd | Wholesale & retail | 2023 |
| Messrs Watson Ltd | Wholesale & retail | 2025 |
| Metal FAB Ltd | Manufacturing | 2005 |
| Metfab Engineering Ltd | Manufacturing | 2019 |
| MG. Mechanical and FAB Ltd | Manufacturing | 2021 |
| MH Farms Ltd | Agriculture & fishing | 2016 |
| MH Reporting Ltd | Health & social care | 2024 |
| Micah T Jones Architect Limited | Professional & scientific | 2019 |
| Micheal Cleasby Limited | Wholesale & retail | 2025 |
| Mick Walker Limited | Information & communication | 2025 |
| Mikam Sound (North) Limited | Administrative & support | 1999 |
| Mikes Fancy Cheese Co Limited | Manufacturing | 2012 |
| Milecross Financial Solutions Limited | Financial services | 2009 |
| Milecross Money Solutions Limited | Financial services | 2009 |
| Mill Lane Homes Ltd | Construction | 2017 |
| Mill Lane Motors Ltd | Wholesale & retail | 2022 |
| Millars Fish N Chips Limited | Hospitality | 2011 |
| Millbank Crescent Quad Management Limited | Households | 2001 |
| Miller Okpro Limited | Wholesale & retail | 2025 |
| Millisle Regeneration | Health & social care | 2015 |
| Millisle Trading CIC | Wholesale & retail | 2017 |
| Millisle Youth Forum | Health & social care | 2012 |
| Millstone (N.I.) Ltd | Wholesale & retail | 2016 |
| Millview Dairy Farm Ltd | Agriculture & fishing | 2024 |
| Millview Wind Limited | Energy | 2015 |
| Mingyu GRA Ltd | Wholesale & retail | 2024 |
| Mini Station Trading Limited | Wholesale & retail | 2024 |
| Minnis Brands Ltd | Wholesale & retail | 2021 |
| Minsheng Trading Ltd | Wholesale & retail | 2024 |
| Mirakee Services Limited | Professional & scientific | 2024 |
| Miss Daisy’S Pets Foods Ltd | Manufacturing | 2025 |
| Mist and Moss Limited | Manufacturing | 2019 |
| MJL Link Ltd | Financial services | 2025 |
| MJS Carpet Cleaning Ltd | Other services | 2020 |
| MK Transport (NI) Limited | Transport & logistics | 2006 |
| MLC Fitness Ltd | Arts & recreation | 2025 |
| Mlle Noey Ltd | Wholesale & retail | 2024 |
| MLTRADING1990 Ltd | Wholesale & retail | 2023 |
| Mlxing Ltd | Manufacturing | 2023 |
| MM Aviation (NI) Ltd | Administrative & support | 2013 |
| MM Group Ireland Limited | Extraterritorial | 1997 |
| MMD Professional Services Ltd | Professional & scientific | 2022 |
| MML SC Limited | Construction | 2015 |
| MNW East Limited | Hospitality | 2024 |
| Mobile Team Adventure Ltd | Arts & recreation | 2011 |
| Mobile Zone Newtownards Limited | Wholesale & retail | 2025 |
| Modulartech Ltd | Professional & scientific | 2021 |
| Moface Ring Limited | Wholesale & retail | 2025 |
| Moisse Ltd | Wholesale & retail | 2025 |
| Molly Browns Hospitality Limited | Hospitality | 2019 |
| Mollys Mews Limited | Construction | 2024 |
| Molnir Automotive Limited | Wholesale & retail | 2026 |
| Moneyrea Properties Ltd | Real estate | 2023 |
| Moneyrea Recovery Services Ltd | Transport & logistics | 2011 |
| Moneyreagh Contracts and Plant Hire Ltd | Construction | 2003 |
| Monomania Ltd | Information & communication | 2026 |
| Mont Corvus Limited | Real estate | 2008 |
| Monty Bracket Ltd | Wholesale & retail | 2026 |
| Mooney's Landscape & Design Ltd | Construction | 2023 |
| Mooning Limited | Manufacturing | 2024 |
| Moorcroft Foods Limited | Manufacturing | 2018 |
| Moorestown Equine Services Limited | Agriculture & fishing | 2022 |
| Moosesee Limited | Wholesale & retail | 2024 |
| More Developement Ltd | Professional & scientific | 2021 |
| Morgan Pearson Ltd | Construction | 2025 |
| Morrow & Company Limited | Real estate | 2004 |
| Moseai Limited | Manufacturing | 2024 |
| Motor Cycle Road Racing Club of Ireland Limited - the | Arts & recreation | 1963 |
| Motorists Insurance Services Limited | Administrative & support | 1993 |
| Motte View Property Management Ltd | Households | 2014 |
| Motto Accessories Limited | Wholesale & retail | 2024 |
| Mottram Collective Ltd | Wholesale & retail | 2025 |
| Mount Eden Management Company Limited | Households | 2019 |
| Mountkai Limited | Wholesale & retail | 2025 |
| Mountpottinger House Management Limited | Real estate | 2005 |
| Moviego Limited | Other services | 2019 |
| Movilla Motors Ltd | Wholesale & retail | 2016 |
| Movilla Woodview Management Limited | Real estate | 1993 |
| Mrpx Limited | Construction | 2010 |
| Mtdreamers Ltd | Extraterritorial | 2021 |
| Muchos Amigos Ltd | Hospitality | 2025 |
| Muer Seker Limited | Wholesale & retail | 2025 |
| Muhasid CET Limited | Wholesale & retail | 2025 |