| Mclaughlin Plant Sales Limited | Wholesale & retail | 2007 |
| Mclernon Estate Agents Ltd | Real estate | 2025 |
| MCM Plant Hire Ltd | Administrative & support | 2011 |
| Mcmackin Contracts Ltd | Administrative & support | 2010 |
| Mcnabb & Co Ltd | Professional & scientific | 2022 |
| Mcnabb Law Ltd | Professional & scientific | 2026 |
| Mcnamee Enterprise Limited | Other services | 2014 |
| MCP Holdings Ltd | Real estate | 2019 |
| MCS Homes Ltd | Construction | 2024 |
| Mcsorley & Co Ltd | Professional & scientific | 2002 |
| Mcsorley Engineering Ltd | Manufacturing | 2022 |
| Mcsorley Enterprises Ltd | Real estate | 1996 |
| Mcwilliamsproperties Ltd | Real estate | 2024 |
| MD Holdings Ireland Ltd | Financial services | 2016 |
| MD Milk Ltd | Wholesale & retail | 2020 |
| MD Poultry Ltd | Agriculture & fishing | 2016 |
| MD Pro Ltd | Construction | 2025 |
| MD Renewables Limited | Wholesale & retail | 2012 |
| MDL Ltd | Transport & logistics | 2020 |
| MDL NI Holdings Ltd | Financial services | 2021 |
| ME Contracts Ltd | Construction | 2014 |
| Meaton Graphics Limited | Information & communication | 2017 |
| Meenagh Contracts Ltd | Construction | 2012 |
| Meenmossagh Utilities Ltd | Construction | 2017 |
| Meitheal Medical Ltd | Health & social care | 2025 |
| MEK Farm Limited | Agriculture & fishing | 2014 |
| Mena Contracts (NI) Ltd | Construction | 2020 |
| Mena Motors Ltd | Wholesale & retail | 2024 |
| Mena Properties Ltd | Real estate | 2023 |
| MEP Manager Limited | Other services | 2012 |
| MET Structures (HR) Limited | Construction | 2021 |
| Metal Deck Ireland Ltd | Manufacturing | 2015 |
| Metberg Ltd | Manufacturing | 2012 |
| Meyler Performance Ltd. | Professional & scientific | 2019 |
| MFE Contracts Ltd | Construction | 2016 |
| MFE Property Ltd | Construction | 2016 |
| MG Marine and Subsea Ltd | Manufacturing | 2023 |
| MG Plant and Machinery Sales UK Ltd | Wholesale & retail | 2014 |
| MG Plant Spares UK Limited | Wholesale & retail | 2023 |
| MGR Group Limited | Administrative & support | 2017 |
| MGS Civils Ltd | Mining & quarrying | 2022 |
| MH Plant Hire (IRL) Ltd | Administrative & support | 2004 |
| Mianlu Ltd | Information & communication | 2024 |
| Michael Doherty Haulage Ltd | Transport & logistics | 2006 |
| Michael Mullan Surgical Services Ltd | Health & social care | 2023 |
| Michael Slattery & Associates Fire Safety Engineers Limited | Public administration | 2007 |
| Midnight Aura Ltd | Professional & scientific | 2025 |
| Mighty Byte Computers Limited | | 2000 |
| Mile One Motors Ltd | Wholesale & retail | 2026 |
| Mill MAC Development Limited | Construction | 1983 |
| Mill Pond Retreat Limited | Other services | 2017 |
| Mill ROW Limited | Manufacturing | 2008 |
| Mills Stewart Ltd | Construction | 2007 |
| Milltown Developments Ltd | Construction | 2014 |
| Milltown Enterprises Limited | Professional & scientific | 2022 |
| Milltown Services Limited | Wholesale & retail | 2015 |
| Mimnagh Contracts Ltd | Construction | 2009 |
| MIT Solutions Group Ltd | Information & communication | 2017 |
| Mixtec TMS Ltd | Manufacturing | 2012 |
| MJ Mcivor Solicitors Ltd | Professional & scientific | 2022 |
| MJ Prestige Ltd | Wholesale & retail | 2012 |
| MJR Fabrications and Developments Ltd | Professional & scientific | 2021 |
| MK Holding 2 Ltd | Financial services | 2024 |
| MK Livestock Ltd | Agriculture & fishing | 2024 |
| MKP Foods Limited | Hospitality | 2022 |
| MKR Properties Ltd | Real estate | 2026 |
| MLE Properties Limited | Real estate | 2020 |
| Mmbj | Real estate | 2021 |
| Mmjni Limited | Financial services | 2018 |
| MMK Independent Social Work Ltd | Health & social care | 2022 |
| MMR Stainless Specialist Ltd | Manufacturing | 2026 |
| Mmrc Enterprises Ltd | Wholesale & retail | 2016 |
| MMS Consultancy (N.I.) Ltd | Construction | 2017 |
| MOD Active Ltd | Arts & recreation | 2018 |
| MOH Contracts Ltd | Construction | 2009 |
| Mollie’S Diner Limited | Hospitality | 2018 |
| Molloy Butchers Ltd | Wholesale & retail | 2014 |
| Monitr Ltd | Information & communication | 2024 |
| Monmar Properties Ltd | Real estate | 2021 |
| Montague Accountancy Services Ltd | Professional & scientific | 2025 |
| Montague Builders Ltd | Construction | 2019 |
| Montilly Hospitality Ltd | Hospitality | 2019 |
| MOO Milk Limited | Agriculture & fishing | 2012 |
| Moody Collective Ltd | Wholesale & retail | 2024 |
| Moody Lemon Ltd | Wholesale & retail | 2023 |
| Moore Energy Ltd | Agriculture & fishing | 2011 |
| Moore Timber Ltd | Agriculture & fishing | 2015 |
| More Power to Your Elbow Ltd | Arts & recreation | 2024 |
| Morgan Dickson (Newry) Limited | Financial services | 2002 |
| Morient Limited | Professional & scientific | 2022 |
| Morris Polythene Greenhouses Ltd | Manufacturing | 1997 |
| Mortgage & Property Plus Limited | Financial services | 2016 |
| Mountain Crescent Company Limited | Real estate | 2017 |
| Mountcass Development Ltd | Financial services | 2021 |
| Mountcass HR Developments Ltd | Real estate | 2024 |
| Mountfield Area Development Association Ltd | Administrative & support | 2017 |
| Mountjoy East Limited | Construction | 2015 |
| Mountjoy Filling Station Ltd | Wholesale & retail | 2015 |
| Mourne NTS Ltd | Real estate | 2012 |
| Mourne Ventures Ltd | Hospitality | 2025 |