| MEG Health & Research NI Limited | Health & social care | 2026 |
| Mega Self Storage Limited | Other services | 2020 |
| Melter Limited | Hospitality | 2021 |
| Melter Restaurants Limited | Financial services | 2019 |
| Merchant Trade Ltd | Wholesale & retail | 2017 |
| Merdyn Limited | Health & social care | 2001 |
| Merlin Holdco Limited | Professional & scientific | 2017 |
| Merlin Productions Ltd | Information & communication | 2016 |
| Merlin Propco Limited | Real estate | 2020 |
| Merlin Topco 1 Limited | Professional & scientific | 2017 |
| Merlin Topco 2 Limited | Professional & scientific | 2017 |
| Merlin Topco 3 Limited | Professional & scientific | 2017 |
| Merlin Woods Limited | Financial services | 2025 |
| MET Metals Ltd | Manufacturing | 2015 |
| Michael Cooper Limited | Professional & scientific | 2006 |
| Michael Foster TV Ltd | Information & communication | 2016 |
| Michael Hoey Auto Ltd | Financial services | 2022 |
| Mildred Property Limited | Real estate | 2016 |
| Mill Management (NO:1) Limited | Extraterritorial | 2013 |
| Mindful Massage Holywood Ltd | Professional & scientific | 2026 |
| Mindful Massage Limited | Professional & scientific | 2018 |
| Mint 13 Limited | Administrative & support | 2021 |
| Mint Hospitality Holdings Limited | Financial services | 2020 |
| MJP Technologies Ltd | Information & communication | 2018 |
| MKR Welding Ltd | Professional & scientific | 2021 |
| MMC Recruitment Solutions Ltd | Administrative & support | 2021 |
| Mobile Equipment Enclosures Limited | Manufacturing | 1999 |
| Modest Beer Brewing Company Limited | Manufacturing | 2023 |
| Mortgage IQ Limited | Financial services | 2005 |
| Motorsport Medical Limited | Health & social care | 2016 |
| Mountainbrook Limited | Real estate | 2015 |
| MP Engineering Consulting Limited | Administrative & support | 2013 |
| MP Rowland Limited | Other services | 2022 |
| MPC Properties (N.I.) Limited | Real estate | 2018 |
| MS Stores (NI) Ltd | Wholesale & retail | 2009 |
| MSC Promotions Limited | Administrative & support | 2011 |
| Multi-View Operations Ltd | Information & communication | 2025 |
| Mura's Meadow Nature Reserve Limited | Arts & recreation | 2026 |
| Murlough Properties Limited | Real estate | 2004 |
| Murrays Exchange Limited | Real estate | 2015 |
| MV Aesthetics Limited | Other services | 2025 |
| Myrtle Investments Limited | Real estate | 2017 |
| N J Medical Services Ltd | Health & social care | 2023 |
| N.I.W. (Services) Ltd | Professional & scientific | 2005 |
| National Museums Northern Ireland Enterprises Limited | Wholesale & retail | 2008 |
| Neil Gillespie Limited | Manufacturing | 2011 |
| Nelson's of Hillsborough Limited | Real estate | 1967 |
| Netherwatch Ltd | Extraterritorial | 2023 |
| Neuro Physio at Home Ltd | Health & social care | 2018 |
| Neve Entertainment Ltd | Information & communication | 2021 |
| New Charm Inns Limited | Hospitality | 2016 |
| Newco 1111 Ltd | Construction | 2011 |
| Newry Sports Coaching Limited | Education | 2018 |
| Newtownbreda Estates Limited | Real estate | 1963 |
| Nexus IT Ltd | Information & communication | 2025 |
| NG Developments a Limited | Real estate | 2024 |
| NG Developments B Limited | Real estate | 2024 |
| NI Friends of Romania Limited | Administrative & support | 2025 |
| NI Hub Limited | Administrative & support | 2023 |
| NI Medicolegals Ltd | Health & social care | 2020 |
| NI Streetwear Collective Limited | Wholesale & retail | 2019 |
| NI683178 Ltd | Wholesale & retail | 2021 |
| Nicholson Enterprises Limited | Financial services | 2017 |
| Nicholson Properties (NI) Limited | Administrative & support | 2025 |
| Nicholson Properties Limited | Real estate | 2017 |
| Nick Moffett Design Limited | Professional & scientific | 2016 |
| Nicon Construction Limited | Construction | 2002 |
| Nidco Ltd | Other services | 2016 |
| Nimrod Computing Ltd | Information & communication | 1997 |
| Nine Ninety One Limited | Professional & scientific | 2026 |
| Nirpoa Ltd | Other services | 2019 |
| Nitc Europe Ltd. | Professional & scientific | 2012 |
| NJ2018 Limited | Wholesale & retail | 2018 |
| Nmq-One Limited | Construction | 2021 |
| Noble@Home Limited | Hospitality | 2020 |
| North Down Health Hub Limited | Construction | 2023 |
| North Down Physio Ltd | Health & social care | 2016 |
| Northern Attitudes Dance Company Limited | Arts & recreation | 2024 |
| Northern Ireland Museums Council | Arts & recreation | 1993 |
| Northern Loft Insulation Ltd | Construction | 2010 |
| Northmount Developments Limited | Information & communication | 2013 |
| Northwise Partners LLP | | 2015 |
| Norwich House Developments Limited | Construction | 2015 |
| Nouveau Holywood Ltd | Hospitality | 2025 |
| Number Seven Ardmore Terrace Limited | Households | 2019 |
| Number SIX Limited | Households | 1991 |
| O'Gorman Private Limited | Financial services | 2023 |
| Oak Hill Imaging Limited | Administrative & support | 2021 |
| Oakey Dokey Day Care Ltd | Health & social care | 2015 |
| Oaktree Medical Ltd | Health & social care | 2024 |
| Obarcs (ABC) Ltd | Real estate | 2019 |
| Obarcs Developments Ltd | Construction | 2021 |
| Obarcs NO 4 (Sterling) Ltd | Real estate | 2005 |
| Oberon Estates Limited | Professional & scientific | 2005 |
| ODO Productions 2 Limited | Information & communication | 2023 |
| ODO Productions Limited | Information & communication | 2020 |
| ODO Rights Limited | Information & communication | 2019 |
| OEW Productions Ltd | Arts & recreation | 2007 |
| Ohmonka Limited | Health & social care | 2014 |
| Old Channel 21 Ltd | Real estate | 2007 |