| M & K Painting and Decorating Limited | Construction | 2014 |
| M & R Contracts Ltd | Administrative & support | 2024 |
| M C Precision Joinery Ltd | Construction | 2020 |
| M C Scaffolding Ltd | Construction | 2022 |
| M Dooher Groundworks and Civils Ltd | Construction | 2014 |
| M L Electrics Limited | Construction | 2018 |
| M Mcdermott Limited | Wholesale & retail | 2015 |
| M Mcfadden Contracts Ltd | Construction | 2022 |
| M O'Neill Transport Ltd | Transport & logistics | 2013 |
| M&C NI Holdings Ltd | Financial services | 2021 |
| M-Tech Solutions Ireland Ltd | Construction | 2013 |
| Mace Engineering Consultancy LLC | | 2000 |
| MAG NI Holdings Ltd | Financial services | 2021 |
| Maguire Brothers Contracts Limited | Construction | 2014 |
| Maguire International Ltd | Transport & logistics | 2025 |
| Maguire Plant Hire Limited | Administrative & support | 2014 |
| Maguire Property Holdings Ltd | Real estate | 2022 |
| Maguire Scaffolding Services Ltd | Construction | 2024 |
| Marc Murray Contracts Ltd | Construction | 2023 |
| Marchbridge Limited | Professional & scientific | 2015 |
| Marcon Developments Ltd. | Construction | 2024 |
| Maria Mccullagh Physiotherapy and Sports Injury Clinic Ltd | Health & social care | 2014 |
| Mark Gormley Ltd | Wholesale & retail | 2011 |
| Mark James Menswear Ltd | Wholesale & retail | 2006 |
| Mark Kelly Joinery Limited | Construction | 2022 |
| Mark Mccrabbe Haulage Ltd | Transport & logistics | 2016 |
| Masala Restaurant Strabane Limited | Hospitality | 2015 |
| Masala Strabane Ltd | Hospitality | 2013 |
| Maxlite (N.I.) Limited | Construction | 2019 |
| Maxlite Lighting & Interiors Ltd | Wholesale & retail | 2025 |
| MC Cabe Logistics Limited | Transport & logistics | 2015 |
| MC Elchar International Transport (N.I.) Limited | Transport & logistics | 2021 |
| MC Gavigan Decor Ltd | Construction | 2023 |
| MC Gavigan Meats Limited | Wholesale & retail | 2021 |
| MCB Builders Ltd | Construction | 2018 |
| Mccaffrey Motors Ltd | Wholesale & retail | 2018 |
| Mccolgans Foodhalls Ltd | Wholesale & retail | 2020 |
| Mcconnell Decor Ltd | Construction | 2025 |
| Mccormick Builders (Donegal) Ltd | Construction | 2021 |
| Mccormick Properties (N.I) Limited | Real estate | 2016 |
| Mccrabbe Farms Ltd | Agriculture & fishing | 2023 |
| Mccrabbe Garage Ltd | Wholesale & retail | 2017 |
| Mccrory Contracts Ltd | Construction | 2016 |
| Mcelhinney Motors (NI) Limited | Wholesale & retail | 2015 |
| MCG Construction Safety Services Ltd | Construction | 2022 |
| Mcgettigan Holdings Ltd | Real estate | 2016 |
| Mcgettigan Homes Ltd | Construction | 2016 |
| Mcgettigan Properties Ltd | Construction | 2020 |
| Mcgill Decor Ltd | Construction | 2021 |
| Mcgill Engineering (IRE) Ltd | Manufacturing | 2019 |
| Mcginty Plant Hire Limited | Administrative & support | 2015 |
| Mcglynn Transport Limited | Transport & logistics | 2014 |
| Mcgowan BUS Hire Limited | Administrative & support | 2015 |
| Mcguigan Courier Network Ltd | Transport & logistics | 2019 |
| Mcha Carwash Ltd | Administrative & support | 2025 |
| Mchugh's OIL Ltd | Other services | 2003 |
| Mchughs Tyres and Fuel Ltd | Other services | 2012 |
| Mcintyre Electric Gates NI Limited | Professional & scientific | 2021 |
| Mckinney Safety Centre Limited | Construction | 2015 |
| Mclaughlin Tiles and Bathrooms Ltd | Wholesale & retail | 2020 |
| MCM Automotive Ltd | Wholesale & retail | 2015 |
| Mcmenamin Construction Ltd | Construction | 2014 |
| Mcmenamin Steel (IRL) Ltd | Construction | 2025 |
| Mcmenamin Steel (NW) Limited | Construction | 2018 |
| Mcmullan Autobreakers Limited | Wholesale & retail | 2013 |
| MCS Civil Engineering Ltd | Construction | 2010 |
| MD Concreting Ltd | Construction | 2017 |
| MD Salvage Limited | Wholesale & retail | 2020 |
| MD Wrap Tools Ltd | Manufacturing | 2024 |
| Mdpconnolly Ltd | Transport & logistics | 2025 |
| Melmount Ltd | Construction | 2013 |
| Mercedes Wedding Car Hire Limited | Transport & logistics | 2015 |
| Meritcom Limited | Information & communication | 2000 |
| Messy Art Ltd | Wholesale & retail | 2025 |
| Messy Moes Ltd | Wholesale & retail | 2020 |
| Miakk Trading Ltd | Wholesale & retail | 2024 |
| Mill View Cars Ltd | Wholesale & retail | 2025 |
| Millgarvan Properties Limited | Real estate | 2017 |
| Milltown Sales Ltd | Wholesale & retail | 2014 |
| Millview Construction Limited | Construction | 2005 |
| ML Trading NW Limited | Wholesale & retail | 2018 |
| MMC Accountancy Ltd | Professional & scientific | 2018 |
| MO Chara's Bar Ltd | Hospitality | 2025 |
| Modern Digital Limited | Information & communication | 2022 |
| Moduframe Ltd | Construction | 2026 |
| Monroe Facilities Ltd | Real estate | 2017 |
| Monroe Property Ltd | Real estate | 2025 |
| Monroe Ventilation Hygiene Services Limited | Administrative & support | 2024 |
| Mooretec Ireland Ltd | Information & communication | 2009 |
| Morpeth Jetsan Ltd | Information & communication | 2023 |
| Mossey Enterprises Limited | Extraterritorial | 2013 |
| Motorparts (Strabane) Ltd | Wholesale & retail | 2004 |
| Mourne Building Services Limited | Construction | 2018 |
| Mourne Legal Limited | Professional & scientific | 2022 |
| Mourne Recycling Ltd | Water & waste | 2009 |
| Mourne Scaffolding Limited | Construction | 2013 |
| Mourneside Dental Practice Limited | Health & social care | 2023 |
| Muldoon Brothers LLP | | 2007 |
| Mulhern Property Maintenance Limited | Construction | 2014 |
| Mulhern Transport (NI) Ltd | Construction | 2024 |