| Millhill Wholesale Ltd | Manufacturing | 2026 |
| Millrace (Dungannon) Management Ltd | Households | 2020 |
| Milo Contracts Ltd | Construction | 2018 |
| Mind My Mortgage Ltd | Financial services | 2020 |
| Mintyrock Film Ltd | Information & communication | 2024 |
| Miskimmons Ltd | Construction | 2019 |
| Miss MAC Dance Studio Ltd | Arts & recreation | 2025 |
| Mitchell & Co of Belfast Ltd | Manufacturing | 2015 |
| Mitchell and Kane Independent Financial Advisers Ltd | Financial services | 2006 |
| Mitchell M Limited | Wholesale & retail | 2014 |
| Mitech Design Ltd. | Professional & scientific | 2018 |
| MJC Maintenance Limited | Construction | 2026 |
| MJL Property Enterprises Ltd | Financial services | 2012 |
| MJM Boiler Services Ltd | Other services | 2022 |
| MK Furnishings Kids Beds Ltd | Manufacturing | 2023 |
| MLH Autos Ltd | Wholesale & retail | 2024 |
| MLS Mortgages Limited | Financial services | 2012 |
| MM Food Solutions Ltd | Hospitality | 2021 |
| MMC Estates Ltd | Households | 2023 |
| Mmcpl Ltd | Hospitality | 2014 |
| MMG Quantity Surveyors Ltd | Professional & scientific | 2020 |
| Mmtl Limited | Transport & logistics | 2015 |
| MO & SA Ltd | Transport & logistics | 2021 |
| Mobile Inn Limited | Wholesale & retail | 2025 |
| Modaz Ltd | Manufacturing | 2026 |
| Modzaprint Ltd | Manufacturing | 2024 |
| Moira Cosmetic Dental Limited | Health & social care | 2015 |
| Moira Foot Clinic Ltd | Other services | 2020 |
| Moira Homes Ltd | Real estate | 2025 |
| Moira Inns Limited | Real estate | 1984 |
| Moira Tyres & Supplies Ltd | Wholesale & retail | 2020 |
| Moirapizzeria Limited | Hospitality | 2023 |
| Mollmac Holdings Limited | Financial services | 2020 |
| Momina Shahid Ltd | Wholesale & retail | 2022 |
| Monarch Property Group Ltd | Real estate | 2020 |
| Monarch Property Rentals Ltd | Real estate | 2023 |
| Monclone Developments Limited | Households | 2020 |
| Money Matters (NI) Limited | Financial services | 2003 |
| Monree Ltd | Professional & scientific | 2022 |
| Moon Gelato Ltd | Manufacturing | 2023 |
| Moore Cleaning Services Ltd | Water & waste | 2026 |
| Moore Mechanical Contracts Ltd | Construction | 2024 |
| Moorefield Investments Limited | Construction | 2017 |
| Mora Water Systems UK Ltd | Extraterritorial | 2015 |
| Morgan Mclernon Telford Ltd | Transport & logistics | 2012 |
| Morla Holdings Ltd | Financial services | 2021 |
| Morning Buzz Ltd | Hospitality | 2025 |
| Morning Star Foundation | Professional & scientific | 2008 |
| Morrison Holden Mortgage & Insurance Solutions Limited | Financial services | 2015 |
| Morrisons Smart Repair (NI) Ltd | Wholesale & retail | 2025 |
| Morrow Portadown Limited | Professional & scientific | 2010 |
| Moss Lane Mgmt Ltd | Households | 2017 |
| Mossvet Limited | Wholesale & retail | 1994 |
| Mossview Management Limited | Households | 2005 |
| Motorbility Components Engineering Ltd | Wholesale & retail | 2015 |
| Motorsport Supplies Ltd | Wholesale & retail | 2021 |
| Motorway Tyres and Accessories Limited | | 1994 |
| Mount Prospect Poultry Limited | Agriculture & fishing | 2016 |
| Mourne Capital Group Limited | Construction | 2015 |
| Mourne Capital Investments Limited | Information & communication | 2017 |
| Mourne Mechanical Services Ltd | Construction | 2023 |
| Mourne Projects Limited | Construction | 2018 |
| Mourneview Meats Limited | Wholesale & retail | 2005 |
| MOY Demesne Management Limited | Households | 2014 |
| MOY Park (Bondco) PLC | Manufacturing | 2014 |
| MOY Park (Newco) Ltd | Manufacturing | 2014 |
| MOY Park Holdings (Europe) Limited | Professional & scientific | 2008 |
| MOY Park Limited | Manufacturing | 1961 |
| MP Mclernon Transport Ltd | Transport & logistics | 2023 |
| MPC Trading Ltd | Agriculture & fishing | 2019 |
| MPH Motors Limited | Wholesale & retail | 2023 |
| MPM Resourcing Ltd | Administrative & support | 2019 |
| MR BOB Holdings Ltd | Financial services | 2022 |
| MR Property Lettings Ltd | Real estate | 2025 |
| MRM Bread Supplies Limited | Transport & logistics | 2025 |
| Mrps Brothers Ltd | Hospitality | 2026 |
| MS Engage Ltd | Professional & scientific | 2024 |
| MSC AM 1 Ltd | Real estate | 2023 |
| MSC WP Ltd | Real estate | 2023 |
| MT Transport (Lurgan) Ltd | Transport & logistics | 2024 |
| MTS Sales Ltd | Wholesale & retail | 2020 |
| MUA Techs Ltd | Information & communication | 2026 |
| MUD Ireland Ltd | Manufacturing | 2019 |
| Mula Group Limited | Financial services | 2015 |
| Mulberry House Retail Ltd | Wholesale & retail | 2022 |
| Mule Trading Ltd | Manufacturing | 2008 |
| Mulhollands Contracts Ltd | Manufacturing | 2018 |
| Mulhollands Grocery Store Ltd | Wholesale & retail | 2013 |
| Mulladry Farm Eggs Ltd | Agriculture & fishing | 2023 |
| Multifix Recycling Ltd | Water & waste | 2007 |
| Multilift Parts Ltd | Wholesale & retail | 2003 |
| Muntak Care Services Ltd | Health & social care | 2026 |
| Murloc Limited | Real estate | 2015 |
| Murtagh Medical Services Limited | Health & social care | 2023 |
| Murtagh Property Ltd | Real estate | 2019 |
| Mutt Wiry Limited | Wholesale & retail | 2024 |
| My Dogs Best Friend Ltd | Other services | 2013 |
| My Health Digital Ltd | Health & social care | 2021 |
| Myco-Farms Ltd | Agriculture & fishing | 2025 |
| Myinicio Limited | Wholesale & retail | 2024 |