| MGT NI Contracts Ltd | Construction | 2019 |
| Miccon Limited | Financial services | 2011 |
| Michael Dunlop Racing Ltd | Arts & recreation | 2013 |
| Michael Joseph Martin Limited | Extraterritorial | 2025 |
| MID & East Antrim Agewell Partnership | Health & social care | 2013 |
| MID Antrim 150 Club Limited | Arts & recreation | 2015 |
| MID Antrim Hunt Club Limited | Agriculture & fishing | 1972 |
| MID Antrim Signs Ltd | Manufacturing | 2012 |
| MID Antrim Theatre CIC | Arts & recreation | 2026 |
| MID Antrim Vineyard | Education | 2019 |
| MID Ulster Eats Ltd | Hospitality | 2025 |
| MID Ulster Flooring Limited | Construction | 2013 |
| Mid-Antrim Motor Club Limited | Arts & recreation | 1955 |
| Midas Commercial Properties Ltd | Real estate | 2025 |
| Middletown Coffee Co Ltd | Hospitality | 2015 |
| Mighty Creative Strategy Ltd | Information & communication | 2018 |
| Mighty Touch Services Ltd | Administrative & support | 2025 |
| Milanos Ballymena Ltd | Hospitality | 2017 |
| Milestone Trust Limited | Administrative & support | 1980 |
| Millbrook Gardens (Kilrea) Management Limited | Households | 2023 |
| Millchurch Properties Limited | Real estate | 1977 |
| Millriver Limited | Professional & scientific | 2009 |
| Mint Belfast Ltd | Other services | 2026 |
| Mirador NI 2025 Ltd | Hospitality | 2025 |
| Miraluxe Distribution Limited | Manufacturing | 2015 |
| Mirel Constructions 2022 Ltd | Construction | 2022 |
| Missionary Container Service Trust | Health & social care | 2007 |
| Mitchell & Wilson Financial Planning Limited | Financial services | 2025 |
| Mizo Street Food Ltd | Hospitality | 2025 |
| MJ Campbell Holdings Limited | Financial services | 2024 |
| MJK Contracts Ltd | Construction | 2019 |
| MJM Joinery (N.I.) Ltd | Construction | 2025 |
| MJS Electrical & Maintenance Limited | Construction | 2022 |
| MK Green Energy Limited | Energy | 2015 |
| Mkln SYS Consultancy Limited | Information & communication | 2012 |
| MM Builders Ltd | Construction | 2017 |
| MMB Contracks Ltd | Construction | 2019 |
| MMB Haulage Ltd | Transport & logistics | 2019 |
| MMCCA5 Ltd | Professional & scientific | 2024 |
| MMQ Property Ltd | Administrative & support | 2021 |
| MNH Construction Limited | Construction | 2014 |
| Moai Digital Ltd | Information & communication | 2019 |
| Moditions Limited | Manufacturing | 2014 |
| Modular Thinking Limited | Information & communication | 2009 |
| MOH Haulage Ltd | Transport & logistics | 2020 |
| Moin Deliveries Ltd | Transport & logistics | 2024 |
| Monaviesh Developments Limited | Construction | 2015 |
| Moneygran Limited | Manufacturing | 2005 |
| Montalto Farms Limited | Agriculture & fishing | 2017 |
| Montgomery Marine & Manufacturing Ltd | Manufacturing | 2025 |
| Montgomery Partnership Ballymena Ltd | Real estate | 2014 |
| Mood Wood Ltd | Professional & scientific | 2022 |
| Mooney Mechanical Installations Ltd | Construction | 2007 |
| Mooney Plumbing & Heating Ltd | Extraterritorial | 2024 |
| Moore Concrete Products Limited | Manufacturing | 2002 |
| Moore Electrics (Ballymena) Ltd | Wholesale & retail | 2017 |
| Moores Animal Feeds Limited | Manufacturing | 1987 |
| Moorfields Consulting Ltd | Health & social care | 2021 |
| Moorfields Developments (N.I.) Limited | Construction | 2017 |
| Moorfields Plant Ltd | Administrative & support | 2012 |
| Moorfields Trading Limited | Real estate | 2013 |
| Moorings Mediquip Ltd | Wholesale & retail | 2007 |
| Moorings Mediquip UK Ltd | Wholesale & retail | 2001 |
| Moover Limited | Transport & logistics | 2009 |
| Moran Restaurant Limited | Hospitality | 2023 |
| Mortgage Connect (N.I) Ltd | Financial services | 2016 |
| Mortgagewise Financial Ltd | Financial services | 2021 |
| Morton Blair LLP | | 2014 |
| Mossview Farms Ltd | Agriculture & fishing | 2020 |
| Moto GS Ltd | Wholesale & retail | 2011 |
| Motor Sports and Spares | Wholesale & retail | 2020 |
| Motor Zong Limited | Wholesale & retail | 2025 |
| Motorsportandaccessories LLP | | 2020 |
| Mountain Technologies Limited | Professional & scientific | 2017 |
| Mountain View (N.I.) Ltd | Hospitality | 2023 |
| Mounthill Developments Ltd | Construction | 2007 |
| Mountview Partitions Limited | Construction | 2004 |
| Moyle Aesthetics Ltd | Health & social care | 2025 |
| Moyle Transport Ltd | Transport & logistics | 2019 |
| MPC Investments Limited | Real estate | 1996 |
| MR Electrical Engineering Ltd | Professional & scientific | 2024 |
| MR Hullabaloo Ltd | Wholesale & retail | 2018 |
| MRB Autobody Limited | Wholesale & retail | 2025 |
| MRH Renewables Ltd | Energy | 2015 |
| Mrjbk (NI) Limited | Real estate | 2024 |
| MRM Contracts UKI Ltd | Construction | 2015 |
| MSC Venyou Ltd | Real estate | 2022 |
| MTC Media Walls Ltd | Construction | 2026 |
| MTE Solutions Limited | Construction | 2026 |
| MTM Utilities Limited | Construction | 2023 |
| Mulholland Haulage Ltd | Transport & logistics | 2010 |
| Mulholland Scrap Metals Ltd | Water & waste | 2007 |
| Mullan European Ltd | Transport & logistics | 2017 |
| Munjab Group Ltd | Information & communication | 2025 |
| Murlough Investments Limited | Real estate | 1996 |
| Muse Nails & Spa Ltd | Other services | 2026 |
| Museco Limited | Information & communication | 2021 |
| Music Service for Pipes & Drums C.I.C. | Education | 2014 |
| MUY Bien Ltd | Wholesale & retail | 2025 |
| MVM Cleaning Ltd | Administrative & support | 2023 |