| Lorraine Armstrong Interiors Ltd | Manufacturing | 2018 |
| Lough View Estate Management Limited | Households | 2010 |
| Loughermore Developments Limited | Construction | 2020 |
| Loughtilube Farms Ltd | Real estate | 2019 |
| Loughview Joinery & Construction Limited | Construction | 2016 |
| LPS Electrical Services Ltd | Construction | 2023 |
| LR Doors Ltd | Construction | 2015 |
| LT Health Ltd | Health & social care | 2024 |
| Lucille's Tea Rooms Limited | Hospitality | 2018 |
| Lumax Trading Limited | Wholesale & retail | 2020 |
| Lyndan Contracts Limited | Construction | 2019 |
| Lynden Gate Limited | Households | 1988 |
| M & B Joinery Services N.I Ltd | Construction | 2021 |
| M&R Estates Limited | Real estate | 2018 |
| M. Culbertson Limited | Extraterritorial | 2009 |
| MAC Joinery Ltd | Construction | 2018 |
| Magheramore Ltd | Construction | 2014 |
| Magheramore Properties Ltd | Real estate | 2026 |
| Magilligan Whiskey Company Limited | Administrative & support | 2018 |
| Mana Fitness Solutions Ltd | Wholesale & retail | 2026 |
| Mannaghco Ltd | Hospitality | 2026 |
| Manorhill Developments Limited | Construction | 2015 |
| Marcol Contracts Limited | Construction | 2014 |
| Marine Solutions Atlantic Ltd | Construction | 2025 |
| Marine View Management Company Limited | Extraterritorial | 2007 |
| Mark Brothers Development Ltd | Construction | 2025 |
| Mark Irwin Electrical Ltd | Construction | 2023 |
| Mark Young Painting Limited | Construction | 2024 |
| Martin Tierney Ltd | Financial services | 2019 |
| Mastercraft Construction (UK) Limited | Construction | 2014 |
| Mastercraft Developments Ltd | Construction | 1997 |
| Maxilla Property Limited | Real estate | 2023 |
| MAY Estates Investment Management Company (Portstewart) Ltd | Households | 2012 |
| Mcaleese Civil Engineering Limited | Professional & scientific | 2015 |
| Mcateer Utilities Ltd | Construction | 2017 |
| Mcauley Group Limited | Financial services | 2021 |
| Mcauley Properties Limited | Real estate | 2021 |
| Mccollum Invest Limited | Financial services | 2024 |
| Mccool Contracts Ltd | Construction | 2006 |
| Mcgee Transport Ltd | Transport & logistics | 2025 |
| Mcgowan Surfacing Ltd | Construction | 2021 |
| Mcgp Limited | Real estate | 2023 |
| Mcgurk Electrics Ltd | Construction | 2015 |
| Mckeever Forestry Limited | Agriculture & fishing | 1983 |
| Mckeever Trading Ltd | Wholesale & retail | 2015 |
| Mckendry (ACL) Limited | Manufacturing | 2014 |
| MCN Electrical Ltd | Construction | 2025 |
| Mcnally Trading Limited | Wholesale & retail | 2025 |
| MCT Utilities Limited | Construction | 2016 |
| MDM Groundworks Ltd | Construction | 2023 |
| Measuretech Ltd | Professional & scientific | 2024 |
| Meatlocker Ltd | Wholesale & retail | 2015 |
| Melroe Limited | Professional & scientific | 2021 |
| Mentupleadup Limited | Information & communication | 2024 |
| Microtec Automation Ltd | Manufacturing | 2001 |
| Midar Investments Limited | Real estate | 2024 |
| Milgro Ltd | Agriculture & fishing | 2003 |
| Mill Cask Limited | Transport & logistics | 2021 |
| Millbank Maintenance Co. Ltd | Construction | 2023 |
| Millbrooke Manor (NO.2) Management Limited | Households | 2013 |
| Millcrun Consulting Limited | Construction | 2017 |
| Millthorne Mews Management Company Limited | Households | 2022 |
| Minipot Properties Limited | Real estate | 2016 |
| MKL Plumbing and Heating Ltd | Construction | 2020 |
| MLS Bike Components Ltd | Wholesale & retail | 2021 |
| MNB Precast Ltd | Construction | 2023 |
| Modern Agility Ltd | Professional & scientific | 2019 |
| Modern Maintenance Solutions Limited | Administrative & support | 2020 |
| Moncrief Eglinton Management Company Ltd | Households | 2024 |
| MOO Town Creamery Ltd | Wholesale & retail | 2020 |
| Moonlight (Limavady) Limited | Hospitality | 2024 |
| Moore Bros Drylining Ltd | Construction | 2016 |
| MOR Groundworks Limited | Construction | 2022 |
| Morrison Associates (NI) Limited | Financial services | 2003 |
| Motorhubni.Com Ltd | Wholesale & retail | 2017 |
| Moving on UP! Training & Personal Development Ltd | Health & social care | 2014 |
| MP Developments (2012) Limited | Extraterritorial | 2012 |
| MQ Contracts Ltd | Construction | 2018 |
| MR Sparkles Cleaning Supplies Ltd | Manufacturing | 2026 |
| Mulkeeragh Farms Ltd | Agriculture & fishing | 2013 |
| Mullan Electrical Limited | Construction | 2018 |
| Mullan Engineering Limited | Construction | 2025 |
| Mullaney Eyecare Ltd | Health & social care | 2012 |
| Mulnally Limited | Financial services | 2024 |
| My Guardian Will Ltd | Professional & scientific | 2025 |
| My Guardian Will Storage Ltd | Administrative & support | 2025 |
| Nass Media Ltd | Manufacturing | 2023 |
| Nass Plant & Construction Ltd | Construction | 2021 |
| Nathan Armstrong Architect Ltd | Professional & scientific | 2020 |
| Nect Limited | Manufacturing | 2012 |
| Need a Tiler Limited | Construction | 2019 |
| New Horizon Developments Limited | Construction | 2017 |
| New Line Elite Cars Limited | Wholesale & retail | 2017 |
| New Line Seating Limited | Wholesale & retail | 2021 |
| New View Electrical Ltd | Construction | 2025 |
| Newcastle Eyecare Limited | Wholesale & retail | 2026 |
| Newline Investments 222 Limited | Wholesale & retail | 2025 |
| Newline Motorhome Hire Limited | Administrative & support | 2023 |
| Newspaper Trade Services Ltd | Wholesale & retail | 2011 |
| Newtownards Eyecare Limited | Wholesale & retail | 2026 |