| Mixopoly Ltd | Hospitality | 2023 |
| MJM Web Solutions Ltd | Information & communication | 2020 |
| MK Creations Limited | Manufacturing | 2015 |
| Mktp Limited | Hospitality | 2021 |
| ML Global Engineering and Infrastructures Limited | Construction | 2025 |
| ML Hughes Construction Ltd | Construction | 2018 |
| ML Hughes Plant Hire Ltd | Administrative & support | 2020 |
| Mlsc Lettings CYF | Real estate | 2024 |
| MM Teleperformance Limited | | 2006 |
| MMI Africa Limited | Hospitality | 2024 |
| MMM Creations Ltd | Arts & recreation | 2023 |
| MMM Design & Build Limited | Construction | 1982 |
| MMM Developments Ltd | Construction | 2004 |
| MMM Newco Ltd | Construction | 2021 |
| MNJ Services Limited | Professional & scientific | 2006 |
| MO House Brew Ltd | Manufacturing | 2020 |
| Mobility Solutions N I Limited | Extraterritorial | 2015 |
| Mocsari Visual Systems Ltd | Administrative & support | 2007 |
| Mode 3 Media Ltd | Information & communication | 2021 |
| Modern Nature Ltd | Manufacturing | 2013 |
| Moduron Pandy Motors CYF | Wholesale & retail | 2004 |
| Mohini Brew & Co. Ltd | Wholesale & retail | 2026 |
| Moir Legal Consultancy LLP | | 2016 |
| Moiranne Lodge Management Company Limited | Extraterritorial | 2020 |
| Molly Brown Consultancy Limited | Professional & scientific | 2026 |
| Molly MOO Designs Limited | Manufacturing | 2014 |
| Momentum Business Development Ltd | Professional & scientific | 2009 |
| Momentum Tax Group Holdings Ltd | Professional & scientific | 2023 |
| Momentum Tax Group Ltd | Other services | 2016 |
| MON Electrical Ltd | Construction | 2023 |
| MON Liquid Screed Limited | Construction | 2025 |
| MON Mariculture Limited | Agriculture & fishing | 2012 |
| MON Mechanical Services Ltd | Wholesale & retail | 2023 |
| MON Naturals Ltd | Manufacturing | 2016 |
| MON Shellfish Limited | Agriculture & fishing | 2015 |
| MON Social Enterprises Ltd | Hospitality | 2012 |
| Moneyreagh Limited | Wholesale & retail | 2010 |
| Montessori Helens Bay Ltd | Health & social care | 2024 |
| Montgomery Quays Ltd | Real estate | 2024 |
| Moore Macdonald & Partners Limited | Professional & scientific | 2005 |
| Moorings Court Limited | Households | 1990 |
| More Adventure Ltd | Administrative & support | 2010 |
| Mornest Caravan Park Limited | Hospitality | 2004 |
| Morrigan Limited | Wholesale & retail | 1998 |
| Morris & Hughes CYF | Construction | 2022 |
| Morrow Estates Limited | Real estate | 2002 |
| Mortgage Buyers Advice Centres Limited | Financial services | 1999 |
| Motor-Tec Auto Motive Ltd | Wholesale & retail | 2005 |
| Motrico Ltd | Information & communication | 2010 |
| Mountain Mead Limited | Manufacturing | 2016 |
| Mountain View Holiday Cottages Ltd | Hospitality | 2018 |
| Mountcastle Estates Limited | Real estate | 2015 |
| Moxin Ltd | Wholesale & retail | 2023 |
| Moyrath House Limited | Extraterritorial | 1988 |
| MP. Developments & Projects Ltd | Construction | 2025 |
| MPO Lets Management Ltd | Hospitality | 2025 |
| MPO Property Ltd | Hospitality | 2024 |
| MPW Making Places Work Limited | Professional & scientific | 2024 |
| MPW Property and Asset Management Limited | Professional & scientific | 2025 |
| MR Laser Ltd | Manufacturing | 2024 |
| MR Street Eats Ltd | Hospitality | 2025 |
| MR Yummy Foods Ltd | Hospitality | 2022 |
| MRB Elite Protection & Maintenance Ltd | Wholesale & retail | 2025 |
| MRG Developments Limited | Real estate | 2002 |
| MRM Technical Solutions Ltd | Construction | 2026 |
| MRM Ventures Ltd | Real estate | 2026 |
| MRS MOP Cleaning Services Ltd | Administrative & support | 2026 |
| MS Bangor Properties Ltd | Real estate | 2020 |
| MS Property 786 Ltd | Real estate | 2025 |
| MS Trading Solutions Limited | Extraterritorial | 2017 |
| MSC Maxwell Holdings Limited | Financial services | 2026 |
| Mseldin Ltd | Other services | 2025 |
| MSK Medical Solutions Ltd | Health & social care | 2023 |
| Mtrc Ltd | Other services | 2011 |
| MTV Traders Ltd | Wholesale & retail | 2022 |
| Mudrock Corp Ltd | Real estate | 2025 |
| Munshigonj Limited | Hospitality | 2019 |
| Munster Simms Engineering Limited | Manufacturing | 1965 |
| Munupay Ltd | Financial services | 2024 |
| Music Education Ltd | Information & communication | 2020 |
| Mustard Construction NI Ltd | Construction | 2022 |
| Mutt Hutt NI Ltd | Professional & scientific | 2015 |
| MW Plastering & Rendering Limited | Construction | 2022 |
| MWJ Mcdowell Consultancy Ltd | Professional & scientific | 2011 |
| MWJ Properties Limited | Construction | 2012 |
| Mynydd Retreat CIC | Education | 2024 |
| Mynydd Timber Service Limited | Agriculture & fishing | 2004 |
| Myrtle Grove Management Company Limited | Households | 2009 |
| Mystery Packet Co Ltd | Real estate | 1986 |
| Myxosoft Limited | Information & communication | 2014 |
| MÔN Seafoods CYF | Extraterritorial | 2010 |
| N I Wines Ltd | Hospitality | 2014 |
| N W Plant Hire (N. Ireland) Limited | Construction | 2013 |
| N&F Wireless & Communications Ltd | Information & communication | 2024 |
| N-Air-G Limited | Professional & scientific | 2011 |
| N.D. Bearings & Transmissions Ltd | Wholesale & retail | 2012 |
| N.I. Fitness Academy Ltd | Education | 2022 |
| N.R. Flats Management Limited | Extraterritorial | 1989 |
| N.S.W Patio Specialist Ltd | Administrative & support | 2024 |
| N.W.W.T. Trading Limited | Wholesale & retail | 1989 |