| Loughview Property Management Limited | Households | 2004 |
| Louise Brogan Ltd | Professional & scientific | 2019 |
| LRC Fire Safety Group Limited | Financial services | 2019 |
| Luha Ltd | Financial services | 2024 |
| Luminai Limited | Information & communication | 2024 |
| Lumino IT Consultancy Ltd | Information & communication | 2025 |
| Luna's Lygophilia Ltd | Arts & recreation | 2021 |
| Lundie Catering Limited | Hospitality | 2005 |
| LUX Temptations Co Ltd | Wholesale & retail | 2024 |
| Luxora Property Limited | Real estate | 2026 |
| Luxory Ltd | Wholesale & retail | 2023 |
| Luxury Details Limited | Other services | 2025 |
| Luxvibe PVT Ltd | Wholesale & retail | 2025 |
| Lyndhurst Plumbing Services Ltd | Construction | 2017 |
| Lynicor Investments Ltd | Financial services | 2021 |
| Lynwen Ltd | Real estate | 2019 |
| Lyttle Software Services Limited | Information & communication | 2017 |
| M & K Partners Ltd | Wholesale & retail | 2025 |
| M & P Bradley Ltd | Construction | 1997 |
| M a Consultancy & Property Developments Ltd | Construction | 2015 |
| M JW Groundworks Ltd | Construction | 2022 |
| M Large Limited | Agriculture & fishing | 2017 |
| M Large Property Ltd | Real estate | 2011 |
| M Large Tree Services Limited | Agriculture & fishing | 1992 |
| M. Cleary T/A ALL UP Ltd | Wholesale & retail | 2024 |
| M.F. Logistics (UK) Ltd | | 2003 |
| M.M.K. Express Limited | Transport & logistics | 1982 |
| M.Macdonald Transport Ltd | Transport & logistics | 2025 |
| M2 Recycling Ltd | Water & waste | 2024 |
| MAC Autoparts Limited | Other services | 2003 |
| MACK5 Limited | Real estate | 2025 |
| Madden Bros Ltd | Construction | 2002 |
| Madurai Homes Ltd | Real estate | 2024 |
| Magical Fairytales Ltd | Arts & recreation | 2025 |
| Magowan Tyres (N.I.) Limited | Wholesale & retail | 1986 |
| Maja Consultancy Ltd | Wholesale & retail | 2026 |
| Majicevents Ltd | Hospitality | 2025 |
| Major Freight Services Ltd | Transport & logistics | 1997 |
| Malayali Heritage Ltd | Other services | 2024 |
| Mallusk Auto Centre Limited | Wholesale & retail | 2003 |
| Mallusk Carparts Ltd | Wholesale & retail | 2011 |
| Management Pro Consulting Ltd. | Professional & scientific | 2024 |
| MAR Foods Belfast Limited | Hospitality | 2017 |
| Marauders Inc Ltd | Arts & recreation | 2023 |
| Maria Furniture Ltd | Manufacturing | 2025 |
| Maritime Quay Management Company Limited | Households | 2018 |
| Mark Blair Music Ltd | Arts & recreation | 2019 |
| Mark Mason Employment Law Ltd | Administrative & support | 2012 |
| Mark One Limited | Professional & scientific | 2023 |
| Mark Wilson Rigging & Lifting Ltd | Professional & scientific | 2023 |
| Marlar Ltd | Wholesale & retail | 2024 |
| Marlo Holmes Ltd | Real estate | 2020 |
| Marmic Limited | Extraterritorial | 2004 |
| Marrog Limited | Other services | 2018 |
| Marshall DC Ltd | Wholesale & retail | 2024 |
| Martin Beatty Consulting Ltd | Information & communication | 2021 |
| Martin Cullen Joinery Ltd | Construction | 2016 |
| Martin Mccarthy Ltd | Information & communication | 2012 |
| Mason Family Holdings Ltd | Financial services | 2026 |
| Masterie Ltd | Professional & scientific | 2025 |
| Mats Properties Ltd | Real estate | 2025 |
| Mauds of Monkstown Limited | Wholesale & retail | 2011 |
| Maxfit Ltd | Arts & recreation | 2019 |
| Maxol OIL Limited | Wholesale & retail | 1935 |
| Mayfield Manor Management Company Ltd | Real estate | 2005 |
| Mayfield Village Community Association | Other services | 2008 |
| Mazars (NI) Limited | Professional & scientific | 2007 |
| Mbni Group Limited | Financial services | 2021 |
| Mbni Holdings Ltd | Financial services | 2019 |
| Mbni Investments Limited | Financial services | 2023 |
| MC Cuisine Ltd | Hospitality | 2020 |
| MC Partitions Limited | Construction | 2017 |
| Mccallan Electrical Solutions Ltd | Construction | 2026 |
| Mccomb's Coach Travel Limited | Transport & logistics | 2012 |
| Mcconnells Markethill Limited | Wholesale & retail | 2019 |
| Mccoubrey Investment Management Ltd | Financial services | 2010 |
| Mccrea Maxus Belfast Limited | Extraterritorial | 2026 |
| Mccullough Building Contractors Ltd | Construction | 2025 |
| Mcdowell Manufacturing Solutions Limited | Manufacturing | 2018 |
| MCG Properties Maintenance Ltd | Real estate | 2019 |
| MCG Property Limited | Real estate | 2017 |
| Mcgimpsey Communications Ltd | Professional & scientific | 2010 |
| Mcgregor Brothers (NI) Limited | Transport & logistics | 2015 |
| Mckee Productions Limited | Information & communication | 2024 |
| Mckeever Hotels Ltd | Hospitality | 2003 |
| Mckibbin 1970 Limited | Extraterritorial | 2013 |
| Mckibbin Holdings Limited | Financial services | 2015 |
| Mckinley Joinery Ltd | Manufacturing | 2023 |
| Mckinley Property Holdings Ltd | Real estate | 2026 |
| Mckr Ltd | Administrative & support | 2018 |
| Mclaughlin & Harvey Holdings Limited | Construction | 2015 |
| Mclaughlin & Harvey Limited | Construction | 1993 |
| MCM Body Repairs (N.I) Ltd | Wholesale & retail | 2026 |
| Mcmullan Bros Ltd | Construction | 2025 |
| MCN Engineering Services Limited | Manufacturing | 2015 |
| Mcnickle Mills Property Ltd | Real estate | 2023 |
| MCS Autosales Limited | Wholesale & retail | 2023 |
| Mcse Limited | Wholesale & retail | 2016 |
| MCX Consultancy Limited | Manufacturing | 2023 |
| MD Upholstery Sofa Makers Ltd | Manufacturing | 2026 |