| Mark Tumilty Design Ltd | Professional & scientific | 2022 |
| Mark W Developments Ltd | Real estate | 2022 |
| Markey Drilling Ltd | Professional & scientific | 2014 |
| Markey Electrical Ltd | Construction | 2021 |
| Markey Retail Limited | Wholesale & retail | 2025 |
| Markey Trenchless Ltd | Professional & scientific | 2014 |
| Marmac N.I. Limited | Construction | 2007 |
| Marshes Maintenance Co Limited | Administrative & support | 2014 |
| Martin Burns Management Consultancy Ltd | Professional & scientific | 2003 |
| Martin Crawley Ltd | Construction | 2006 |
| Martin Hardware Limited | Wholesale & retail | 2005 |
| Martin Hiab Haulage Ltd | Transport & logistics | 2017 |
| Martin Kelly Ltd | Wholesale & retail | 2025 |
| Martin Mcginn & Sons Ltd | Agriculture & fishing | 2003 |
| Martin Reel Ltd | Agriculture & fishing | 2002 |
| Martin Ryan Radiology Ltd | Professional & scientific | 2009 |
| Martin Woods Limited | Construction | 2007 |
| Marval Power Holdings Limited | Financial services | 2025 |
| Mary ANN Doyle NI Properties Limited | Other services | 2025 |
| Mashiax Ltd | Real estate | 2025 |
| Master VET Limited | Professional & scientific | 2017 |
| Master's Green Limited | Households | 2017 |
| Mastercraft Joinery Limited | Manufacturing | 2017 |
| Masters Choice Limited | Manufacturing | 2003 |
| Matrix Security Solutions Ltd | Administrative & support | 2019 |
| Matt D'Arcy & Company Limited | Manufacturing | 2015 |
| Matthews Coach Hire NI Ltd | Transport & logistics | 2016 |
| Matthews Joinery Ltd | Construction | 2025 |
| Maturi Fdtdy Ltd | Wholesale & retail | 2025 |
| Maudra Ltd | Other services | 2012 |
| Maverick Socials Ltd | Professional & scientific | 2021 |
| Maxgold Capital L.P. | | 2015 |
| Maxhill Services L.P. | | 2017 |
| Maxi Carpentry Ltd | Construction | 2016 |
| Maxi MIX GAS Systems Limited | Energy | 2021 |
| MAY Developments (N.I.) Ltd | Construction | 2005 |
| MAY Property Management Limited | Real estate | 2018 |
| MAY Rentals Hillsborough Ltd | Real estate | 2021 |
| MAY Rentals Ltd | Real estate | 2014 |
| May-Ard Construction Ltd | Construction | 2025 |
| Maya Cafe Company Ltd | Wholesale & retail | 2011 |
| Maya Coffee Limited | Hospitality | 2016 |
| Mayobridge Community Association Limited | Administrative & support | 1998 |
| Mayobridge Golf Club Limited | Hospitality | 2021 |
| Mayobridge Parish & Heritage Association | Administrative & support | 2009 |
| Maypole Interiors Ltd | Professional & scientific | 2017 |
| Mayson Organization L.P. | | 2015 |
| Maysun Development LP | | 2014 |
| Maytown Ltd | Real estate | 2021 |
| MB Newry Buttercane Ltd | Hospitality | 2026 |
| MB Newry Limited | Hospitality | 2024 |
| MB Progressive Solutions Ltd | Professional & scientific | 2024 |
| MBC Timberframe (UK) Ltd | Construction | 2014 |
| Mbibeh Ltd | Public administration | 2025 |
| Mbog Enterprises Ltd | Wholesale & retail | 2023 |
| MC Build & Construction Ltd | Construction | 2019 |
| MC Conville Funeral Directors Ltd | Other services | 2017 |
| MC Convilles Crossmaglen Ltd | Hospitality | 2023 |
| MC Court Mechanical Services Ltd | Construction | 2023 |
| MC Culture & Experience Ltd | Professional & scientific | 2026 |
| MC Developments Ltd | Construction | 2013 |
| MC Foods Camlough Ltd | Hospitality | 2012 |
| MC Geough Metals UK Ltd | Wholesale & retail | 2020 |
| MC Ginn Farming Enterprises Ltd | Agriculture & fishing | 2015 |
| MC Keown Training Ltd | Education | 2020 |
| MC Manus Agri Hire Ltd | Administrative & support | 2017 |
| MC Manus Energy Ltd | Energy | 2016 |
| MC Nally Distribution and Logistics Limited | Transport & logistics | 2017 |
| MC Nulty Smyth Associates Ltd | Professional & scientific | 2012 |
| MC Shane Contracts Ltd | Wholesale & retail | 2019 |
| MCA Motors Ltd | Wholesale & retail | 2025 |
| Mcal Bricklaying Ltd | Construction | 2025 |
| Mcanuff Transport Ltd | Transport & logistics | 2024 |
| Mcardle Electrical Ltd | Construction | 2026 |
| Mcardle Enterprises Limited | Construction | 2017 |
| Mcardle Meats (NI) Limited | Wholesale & retail | 2013 |
| Mcateer Contract Services Ltd | Construction | 2017 |
| Mcateer Properties Ltd | Real estate | 2024 |
| Mcateer Recycling Ltd | Administrative & support | 2004 |
| MCB Performance Ltd | Wholesale & retail | 2025 |
| Mcbm Limited | Extraterritorial | 2016 |
| Mcbran Property Management Limited | Households | 2007 |
| Mcbride Contractors Limited | Construction | 2003 |
| MCC Build Limited | Construction | 2018 |
| MCC Global Ltd | Administrative & support | 2022 |
| Mccabe Quantity Surveyors Ltd | Professional & scientific | 2023 |
| Mccabes Fine Furnishings Ltd | Wholesale & retail | 2012 |
| Mccambridge Medical Limited | Health & social care | 2025 |
| Mccann Agri Ltd | Agriculture & fishing | 2026 |
| Mccann Bros (N.I.) Ltd | Transport & logistics | 2012 |
| Mccann Motors NI Ltd | Wholesale & retail | 2025 |
| Mccann Teggart Limited | Professional & scientific | 2017 |
| Mccanns Customs Clearance Services Ltd | Transport & logistics | 2020 |
| Mccartan Contracts Limited | Transport & logistics | 2026 |
| Mccarthy Keville O' Sullivan UK Limited | Professional & scientific | 2025 |
| Mccartney Transport Ltd | Transport & logistics | 2026 |
| Mccombe Services & Sons Ltd | Transport & logistics | 2019 |
| Mccomiskey Electrical Engineering Ltd | Construction | 2025 |
| Mccon Limited | Construction | 2017 |
| Mcconville Building Contractors Limited | Construction | 2001 |