| Mdki Properties Ltd | Construction | 2026 |
| MDN Consulting Limited | Professional & scientific | 2017 |
| MEC Software Solutions Ltd | Information & communication | 2024 |
| Mechanexpert Limited | Extraterritorial | 2016 |
| MEDAID4KIDS | Health & social care | 2011 |
| Medi Cosmetic Aesthetic Skin Care Clinic Limited | Other services | 2019 |
| Meeting Centres Together CIC | Health & social care | 2026 |
| Mega Sunbeds Ltd | Wholesale & retail | 2021 |
| Menopause Connect NI CIC | Health & social care | 2024 |
| Merchant Services Belfast Limited | Financial services | 2017 |
| Merkur Operations NI Holdings Limited | Arts & recreation | 2000 |
| Meroc Ltd | Financial services | 2020 |
| Method Therapies Ltd | Health & social care | 2023 |
| Metro Holidays Ltd | Real estate | 2024 |
| MFP Properties Ltd | Real estate | 2023 |
| MG Residential Investments Limited | Real estate | 2021 |
| MG Restaurants and Coffee Shop Ltd | Hospitality | 2025 |
| Mgjc T4L Limited | Information & communication | 2023 |
| MI Life Coaching Ltd | Professional & scientific | 2025 |
| MIA Piel Skincare Limited | Health & social care | 2023 |
| Michael Stevenson Consulting Ltd | Professional & scientific | 2012 |
| Michael Walker Consulting Limited | Professional & scientific | 2010 |
| Micromax Machinery Group Ireland Ltd | Manufacturing | 2023 |
| Midmar LLP | | 2014 |
| Mielea Holdings Ltd | Wholesale & retail | 2025 |
| Milan Contracts Limited | Construction | 2020 |
| Mill Bridge Consulting Limited | Professional & scientific | 2022 |
| Millars Retail (Ireland) Limited | | 1997 |
| Miltons Bath Repair and RE Enamelling Ireland Limited | Other services | 2025 |
| Mindful Hummingbird CIC | Health & social care | 2024 |
| Ming's Happiness Ltd | Hospitality | 2023 |
| Minnie Dutch Pancakes Ltd | Hospitality | 2025 |
| Minta Property Sales Ltd | Real estate | 2023 |
| Mirabilis Health Limited | Professional & scientific | 2023 |
| Mirra AI Technologies Ltd | Information & communication | 2025 |
| Mitawon Limited | Wholesale & retail | 2025 |
| Mitchell Property Management Ltd | Real estate | 2007 |
| MJ Reed Technology Ltd | Information & communication | 2026 |
| MJM Business Growth Services Ltd | Professional & scientific | 2024 |
| MM Cleaning Services Limited | Administrative & support | 2024 |
| MM4 Solutions Ltd | Information & communication | 2010 |
| MMA Autos Limited | Wholesale & retail | 2023 |
| MMG Restaurants Ltd | Hospitality | 2021 |
| MNF Civils Ltd | Professional & scientific | 2020 |
| MNF Clean Energy Ltd | Extraterritorial | 2021 |
| Mobile Locs Salon Ltd | Other services | 2025 |
| Modern Evolved Products Limited | Manufacturing | 2011 |
| Modern Money Ltd | Professional & scientific | 2020 |
| Modus Architectural Limited | Professional & scientific | 2021 |
| MOF Technologies Limited | Manufacturing | 2012 |
| Moizae Ltd | Manufacturing | 2026 |
| Mojoni Ltd | Other services | 2022 |
| Monkstown Apartments Management Co Ltd | Extraterritorial | 2007 |
| Monkstown Boxing Club | Arts & recreation | 2006 |
| Monkstown Community Forum | Administrative & support | 1995 |
| Montana Real Estate Ltd | Real estate | 2022 |
| Montgomery Distribution Limited | Transport & logistics | 2003 |
| Montgomery Freight Management Limited | Transport & logistics | 2018 |
| Montgomery Tank Services Limited | Transport & logistics | 1980 |
| Mossley Export Ltd | Other services | 2020 |
| Motach Ltd | Health & social care | 2023 |
| Motibo Marketing Ltd | Professional & scientific | 2024 |
| Motion Granules Ltd | Water & waste | 2018 |
| Mount Pleasant House (NI) Limited | Households | 2006 |
| Mourne Living Ltd | Wholesale & retail | 2024 |
| Mourneview Catering Ltd | Hospitality | 2026 |
| MPG Property Solutions Limited | Real estate | 2025 |
| MR. Sparrow Ltd. | Transport & logistics | 2026 |
| MRC Core Holdings Ltd | Financial services | 2026 |
| MS Groceries Wholesale Ltd | Wholesale & retail | 2026 |
| Mukul Asian Foods Limited | Hospitality | 2025 |
| Mulberry Bush Playgroup | Education | 2005 |
| Mulholland Bros. (Brick and Sand) Limited | Extraterritorial | 1973 |
| Mullan Couriers Ltd | Transport & logistics | 2021 |
| Mullzo's Pizza Ltd | Hospitality | 2021 |
| Multi Packaging Solutions NI Limited | Professional & scientific | 1983 |
| Mulvenna (Holdings) Limited | Real estate | 1969 |
| Munish Property & Rental Ltd | Real estate | 2003 |
| Murphy's Stores Limited | Wholesale & retail | 2021 |
| Mushtaq Financial Ltd | Wholesale & retail | 2025 |
| My Property Pros (Newtownabbey) Ltd. | Administrative & support | 2023 |
| Myfit Limited | Arts & recreation | 2017 |
| NAE Electrical Ltd | Construction | 2025 |
| Naturologyx Ltd. | Other services | 2013 |
| Nbas Consultants Limited | Professional & scientific | 2015 |
| Nbas Properties Ltd | Real estate | 2021 |
| NCD Courier Ltd | Transport & logistics | 2024 |
| Neill Naval Architecture Ltd | Professional & scientific | 2026 |
| Nena Investments Ltd | Real estate | 2015 |
| Nesbitt Grass Machinery Ltd | Manufacturing | 2023 |
| Network Auto Store Limited | Wholesale & retail | 2017 |
| Neuroit Force Limited | Information & communication | 2025 |
| New Beginnings 517 Ltd | Extraterritorial | 2023 |
| New World Systems (Belfast) Limited | | 1997 |
| Newline Mechanical Services Ltd | Construction | 2007 |
| Newtown Diner Limited | Hospitality | 2023 |
| Newtownabbey Footgolf Ltd | Arts & recreation | 2021 |
| Newtownabbey LUX Nails and Spa Ltd | Other services | 2025 |
| Newtownabbey Management Ltd | Households | 2010 |
| Newtownabbey Memorials Ltd | Other services | 2024 |