| MID Ulster Accountants Limited | Professional & scientific | 2018 |
| MID Ulster Claims Ltd | Financial services | 2019 |
| MID Ulster MX Trax Ltd | Arts & recreation | 2013 |
| MID Ulster Procurement Ltd | Administrative & support | 2025 |
| MID Ulster Sweeper Hire Ltd | Construction | 2017 |
| Mid-Ulster Plant Hire Ltd | Administrative & support | 2016 |
| Midway Storage Limited | Real estate | 2017 |
| Milling Farms Ltd | Agriculture & fishing | 2019 |
| Millside Holdings Limited | Financial services | 2022 |
| Millside Investments Limited | Financial services | 2022 |
| Milltown Asset Management Limited | Administrative & support | 2019 |
| Mindtrack 360 Ltd | Information & communication | 2014 |
| Miracle Breakthru Limited | Professional & scientific | 2023 |
| Mirza Farhan Trading Ltd | Wholesale & retail | 2025 |
| MJ Daly Ltd | Construction | 2011 |
| MJ Mcwilliams & Co Ltd | Professional & scientific | 2018 |
| MJH International Consultancy Ltd | Professional & scientific | 2026 |
| MJH Veterinary Ltd | Professional & scientific | 2016 |
| MJI Transport Ltd | Transport & logistics | 2021 |
| Mjmck Ltd | Health & social care | 2026 |
| MJR Holdings Ireland Limited | Financial services | 2022 |
| MJS Cars Ltd | Wholesale & retail | 2019 |
| MJS Garage Services Ltd | Wholesale & retail | 2012 |
| MK Fire Consultants Ltd | Public administration | 2022 |
| MK Holding 1 Ltd | Financial services | 2024 |
| MKE Energy Engineering Ltd | Construction | 2019 |
| MLM Properties Ltd | Real estate | 2013 |
| Mlymdsyxgs Limited | Wholesale & retail | 2025 |
| MMG Buildings Ltd | Construction | 2024 |
| MML Contracts (Dungannon) Limited | Construction | 2012 |
| MML Corporate Holdings Ltd | Financial services | 2022 |
| MML Property Ltd | Real estate | 2022 |
| Mnes Ltd | Manufacturing | 2007 |
| Mocca Baby Ltd | Wholesale & retail | 2021 |
| Modcon Construction Ltd | Construction | 2020 |
| Modern Modular Ltd | Construction | 2025 |
| Mojo Property Ltd | Construction | 2016 |
| Molloy Mechanical Ltd | Construction | 2012 |
| Molly and MIA Community CIC | Health & social care | 2024 |
| Molwal Safety Ltd | Other services | 2025 |
| Mont Brison Limited | Financial services | 2013 |
| Montgomery Poultry Ltd | Agriculture & fishing | 2015 |
| Moody Movement C.I.C. | Wholesale & retail | 2021 |
| Moon & Back Limited | Hospitality | 2026 |
| Moore and Faloon Ltd | Construction | 2023 |
| Moores Quality Hams Limited | Manufacturing | 2024 |
| Moorlaghan Holdings Ltd | Financial services | 2023 |
| Moorlaghan Properties Ltd | Real estate | 2023 |
| Morris Utility Services Ltd | Construction | 2023 |
| Mortgage Angels (NI) Limited | Professional & scientific | 2010 |
| Motor & Commercial Parts Limited | Wholesale & retail | 1994 |
| Mourne Veterinary Clinic Limited | Professional & scientific | 2011 |
| MOY Auto Services Ltd | Wholesale & retail | 2020 |
| MOY Contracts Limited | Construction | 2017 |
| MOY Furniture Limited | Wholesale & retail | 2005 |
| MOY Optical Ltd | Health & social care | 2025 |
| MOY Orthodontic Clinic Ltd | Health & social care | 2011 |
| MOY Safety Solutions Ltd | Construction | 2019 |
| MOY Taxis Limited | Transport & logistics | 2025 |
| MOY Transport Ltd | Transport & logistics | 2010 |
| Moygashel Community Development Association Limited | Other services | 1993 |
| Moyle Engineers Ltd | Manufacturing | 2020 |
| Moylecivil Ltd | Construction | 2026 |
| Moyola Sealant Services Ltd | Construction | 2024 |
| MP Poultry Limited | Agriculture & fishing | 2014 |
| MPD Plumbing & Mechanical Ltd | Construction | 2026 |
| MPH Development Limited | Construction | 2002 |
| MPS Retail Ltd | Wholesale & retail | 2017 |
| MR Car Kits Ltd | Wholesale & retail | 2021 |
| MR Database Solutions Ltd | Information & communication | 2021 |
| Mrhi | Construction | 2020 |
| MRL Dungannon Limited | Financial services | 2026 |
| Msdk Ltd | Information & communication | 2025 |
| MSE Services (N.I.) Ltd. | Manufacturing | 2019 |
| MSJ Contract Holdings Limited | Financial services | 2022 |
| MSJ Contracts Limited | Construction | 2008 |
| MSK Ultrasound Ireland Ltd | Administrative & support | 2025 |
| MSR Fabrications Ltd | Manufacturing | 2023 |
| MSZ Transport Ltd | Transport & logistics | 2026 |
| MT BUS Hire Limited | Transport & logistics | 2025 |
| MT Mccausland Capital Limited | Financial services | 2026 |
| MTC Enterprises Ltd | Administrative & support | 2012 |
| Mtech Engineering & Design Solutions Ltd | Professional & scientific | 2010 |
| MTS Powerco Limited | Manufacturing | 2019 |
| MTX Cloud Services Limited | Information & communication | 2017 |
| Mulboy Farm Ltd | Agriculture & fishing | 2025 |
| Muldoon (GB) Limited | Manufacturing | 2014 |
| Muldoon Holdings Ltd | Financial services | 2017 |
| Muldoon Woodville Ltd | Real estate | 2017 |
| Mulfab Engineering Ltd | Professional & scientific | 2015 |
| Mulgrew Construction and Utilities Ltd | Construction | 2021 |
| Mulgrew Holdings Ltd | Financial services | 2022 |
| Mulgrew Pharmaceutical Services Ltd | Professional & scientific | 2022 |
| Mulla Construction Ltd | Construction | 2002 |
| Mulla Ltd | Construction | 2007 |
| Mullach Glas One Limited | Professional & scientific | 2006 |
| Mullach Glas Three Limited | Extraterritorial | 1939 |
| Mullach Glas Two Limited | Extraterritorial | 1984 |
| Mullaghbawn Retail Ltd | Wholesale & retail | 2023 |
| Mullaghmore Milk Ltd | Agriculture & fishing | 2025 |