| Mallon Technology (Northern Ireland) Limited | Administrative & support | 2000 |
| Mamico Holdings Ltd | Financial services | 2025 |
| Manor Event Catering Ltd | Hospitality | 2025 |
| Manor Forest Products Limited | Agriculture & fishing | 2021 |
| Manor Switchgear & Controls Ltd | Manufacturing | 2022 |
| Martin Developments (Castlederg) Limited | Construction | 2010 |
| Mason Automation Ltd | Professional & scientific | 2021 |
| Maste Properties Limited | Construction | 2013 |
| Matadig Ltd | Professional & scientific | 2019 |
| Maxflow Power Products Limited | Manufacturing | 2001 |
| MBR Contracts Ltd | Construction | 2011 |
| Mc's Snackbox and Catering Services Limited | Hospitality | 2015 |
| Mcaleer & Mcgarrity Mechanical Ltd | Construction | 2022 |
| Mcaleer Music Ltd | Wholesale & retail | 2017 |
| Mccann Contracts Ltd | Construction | 2018 |
| Mccfm Holdings Limited | Financial services | 2025 |
| Mcclure Distribution Ltd | Wholesale & retail | 2012 |
| Mccord Machinery Limited | Wholesale & retail | 2008 |
| Mcgarrity Contracts Ltd | Construction | 2016 |
| Mcgarrity Group Limited | Financial services | 2025 |
| Mcgrath Motors Limited | Wholesale & retail | 2015 |
| Mcgurk Consulting Ltd | Professional & scientific | 2026 |
| Mcgurk Haulage Ltd | Transport & logistics | 2014 |
| Mcivor Truckmixers Ltd | Manufacturing | 2020 |
| Mckenzie Transport Ltd | Transport & logistics | 2021 |
| Mckernan Construction Limited | Construction | 1997 |
| Mcmahon Bros Ltd | Financial services | 2022 |
| MCN Online Shop Ltd | Wholesale & retail | 2021 |
| Mcnmedia(Ni) Ltd | Extraterritorial | 2012 |
| Mcoscar Properties Limited | Real estate | 2023 |
| Mcsorley Commercial Consulting Ltd | Construction | 2025 |
| Mcswiggan Electrical Limited | Manufacturing | 2020 |
| MD Construction and Building Ltd | Construction | 2026 |
| MEC Engineering Ltd | Manufacturing | 2021 |
| Meenan Ltd | Financial services | 2012 |
| Mektronic Limited | Manufacturing | 2022 |
| Memor Esto Limited | Real estate | 2024 |
| Meteor Direct Limited | Wholesale & retail | 2010 |
| Meteor Electrical Limited | Wholesale & retail | 2009 |
| Meteor Holdings Limited | Administrative & support | 2015 |
| Metro Surveillance Group Ltd | Administrative & support | 2012 |
| Metworks Roofing Ltd | Construction | 2024 |
| Mfsmm Ltd | Other services | 2025 |
| MG Pro Events Ltd | Arts & recreation | 2016 |
| MGL Mechanical Limited | Construction | 2023 |
| Michael Costelloe Landscaping Limited | Wholesale & retail | 2024 |
| Micran Joinery Limited | Construction | 2011 |
| MID Ulster Cars Ltd | Wholesale & retail | 2009 |
| MID Ulster Child Contact Centre | Health & social care | 2018 |
| MID Ulster Emsella Clinic Ltd | Health & social care | 2025 |
| MID Ulster Laser Clinic Ltd | Other services | 2023 |
| MID Ulster Victims Empowerment Project (Muve Project) | Education | 2013 |
| Mid-Ulster Rotating Electrics Limited | Manufacturing | 2013 |
| Milcon Services Ltd | Construction | 2025 |
| Mill DAM Developments Limited | Construction | 2010 |
| Mixer Drums UK Ltd | Manufacturing | 2016 |
| Mjdb Restaurants Ltd | Hospitality | 2019 |
| MJP ENT Ltd | Information & communication | 2023 |
| MK Sales and Services Limited | Real estate | 2018 |
| MKH Contracts Ltd | Wholesale & retail | 2021 |
| MMC Utilities & Groundworks Limited | Construction | 2021 |
| MMG Digital Consulting Ltd | Information & communication | 2022 |
| MMI (N.I.) Limited | Construction | 2020 |
| MNH Supplies Ltd | Hospitality | 2022 |
| MOK Heating Services Ltd | Construction | 2025 |
| Molloys Tyres Limited | Wholesale & retail | 2026 |
| Mooney Auto Services Ltd | Wholesale & retail | 2017 |
| Mooney Commercials Ltd | Manufacturing | 2019 |
| Moortown Stores Ltd | Wholesale & retail | 2012 |
| Moorwood Developments Limited | Construction | 2019 |
| MOR Architects Ltd | Professional & scientific | 2022 |
| MOR Associates Ltd | Professional & scientific | 2025 |
| MOR Electrical Ltd | Energy | 2022 |
| Mortgage Services Cookstown Ltd | Financial services | 2020 |
| Moss Developers Limited | Construction | 2011 |
| Motrol Limited | Water & waste | 2017 |
| Mountainhill Enterprises Ltd | Wholesale & retail | 2024 |
| Mountvale Private Nursing Home Limited | Health & social care | 2010 |
| Moykeeran Project Management Limited | Professional & scientific | 2012 |
| MRH Foods Limited | Hospitality | 2024 |
| MRP 200 REN Limited | Real estate | 2020 |
| MRP Capital Limited | Extraterritorial | 2013 |
| MRP Chapel Lane Limited | Construction | 2006 |
| MRP Development Management Limited | Extraterritorial | 2020 |
| MRP Development Services Limited | Extraterritorial | 2021 |
| MRP Developments Limited | Extraterritorial | 2021 |
| MRP Land Limited | Financial services | 2011 |
| MRP Weavers Cross Limited | Construction | 2023 |
| MSD Moortown Ltd | Wholesale & retail | 2026 |
| Mucky Pups Retreat Ltd | Other services | 2024 |
| Mullan Holdings Limited | Real estate | 2019 |
| Mulligan Entertainment Ltd | Hospitality | 2019 |
| Mulnavoo Commercial Limited | Professional & scientific | 2012 |
| Murphy Dental Limited | Health & social care | 2024 |
| My Perfect Sofa Ltd | Manufacturing | 2023 |
| MZ Properties (N.I.) Ltd | Real estate | 2022 |
| N & J Restaurants Ltd | Hospitality | 2019 |
| N & R Repairs Ltd. | Professional & scientific | 2018 |
| Nails & Spa 31 Ltd | Other services | 2024 |
| Nano Developments Holdings Ltd | Real estate | 2016 |