| KJM Electrical Ltd | Construction | 2009 |
| Kkli Ltd | Agriculture & fishing | 2020 |
| Knocksticken Holdings Ltd | Financial services | 2022 |
| Kodiak Films Ltd | Information & communication | 2023 |
| KPS Accountants Limited | Professional & scientific | 2014 |
| KR Equine Veterinary Services Ltd | Professional & scientific | 2021 |
| KT Property Ltd | Real estate | 2025 |
| KTB Events Company Ltd | Information & communication | 2025 |
| Kubbi Imports Ltd | Wholesale & retail | 2025 |
| L.J.C Wines & Spirits Limited | Hospitality | 1966 |
| LA Laser Downpatrick Ltd | Other services | 2024 |
| Lagan Property Services Ltd | Administrative & support | 2025 |
| Lakeview Furniture Ltd | Wholesale & retail | 2022 |
| Land Venture Property Limited | Households | 2025 |
| LCA Building Ltd | Construction | 2015 |
| Leader Contracts Ltd | Construction | 2017 |
| Learn to JIG Ltd | Arts & recreation | 2023 |
| Lecale Brewery Limited | Manufacturing | 2017 |
| Lecale Clinic Ltd | Health & social care | 2025 |
| Lecale Contracts Limited | Construction | 2004 |
| Lecale Distribution Limited | Households | 2018 |
| Lecale Energy Ltd | Real estate | 2022 |
| Lecale Group Ltd | Agriculture & fishing | 2002 |
| Lecale Harvest Ltd | Manufacturing | 2020 |
| Lecale Heritage Management Ltd | Construction | 2026 |
| Legnegoppack Farms Limited | Agriculture & fishing | 2014 |
| Lenor Limited | Agriculture & fishing | 2012 |
| Lesley Holywood Properties Limited | Construction | 2020 |
| Let's DO Veterans Support & Rehabilitation Limited | Administrative & support | 2015 |
| Lidr Ltd | Information & communication | 2025 |
| Life Change Changes Lives | Health & social care | 2015 |
| Lightbody Design Ltd | Professional & scientific | 2012 |
| Lighthouse Electrical Contracts Limited | Construction | 2017 |
| Linden Clad UK Ltd | Construction | 2017 |
| Lineage Coffee Ltd | Hospitality | 2024 |
| Little Mustard Seed Ltd | Financial services | 2025 |
| LM Prima Consultancy Co Ltd | Professional & scientific | 2024 |
| LN Services Ltd | Other services | 2006 |
| Localjobsni Ltd | Information & communication | 2018 |
| Logh Property Limited | Real estate | 2024 |
| Logue Casings Limited | Manufacturing | 1996 |
| Lomond Real Estate Limited | | 2004 |
| Look Outdoor Limited | Professional & scientific | 2022 |
| Lough Ford Properties Ltd | Real estate | 2024 |
| Loughinisland Rural Development C.I.C. | Administrative & support | 2024 |
| Loughshore Physiotherapy Ltd | Arts & recreation | 2020 |
| Lowry Transport Ltd | Transport & logistics | 2026 |
| Lucelle Group Ltd | Information & communication | 2025 |
| Lumitech Lighting Limited | Professional & scientific | 2024 |
| Lynn's Country Foods Limited | Manufacturing | 1987 |
| Lynsey Mcilwaine Make-Up Ltd | Other services | 2023 |
| M C Dental Laboratory Limited | Manufacturing | 2017 |
| M C V Conversions Limited | Other services | 2014 |
| M Polly Contracts Ltd | Construction | 2019 |
| M R & E Properties Limited | Real estate | 2025 |
| M&J Practical Ltd | Other services | 2020 |
| MAC Millan of Crossgar Limited | Manufacturing | 1956 |
| Macnabb Analytics Ltd | Information & communication | 2025 |
| Magee Farming Ltd | Agriculture & fishing | 2014 |
| Magna Moon Limited | Administrative & support | 2016 |
| Main Community Enterprises CIC | Health & social care | 2025 |
| Mainstay DRM Ltd | Health & social care | 2007 |
| Mainstay DRP | Health & social care | 1990 |
| MAK Developments Ltd | Construction | 2004 |
| Making Memories 4U Ltd | Wholesale & retail | 2022 |
| Marine Projects Ireland Ltd | Transport & logistics | 2019 |
| Martin's Moffat Farm Ltd | Real estate | 2023 |
| Mascon Business Advisory Ltd | Information & communication | 2011 |
| Mascon Holdings (NI) Limited | Financial services | 2016 |
| Mascon Properties Limited | Real estate | 2016 |
| Maven Safety Consultancy Limited | Professional & scientific | 2020 |
| MB Architectural Design Services Limited | Professional & scientific | 2017 |
| MB Pizza Limited | Hospitality | 2024 |
| Mcas Developments Ltd | Construction | 2014 |
| Mccann Aero Ltd | Manufacturing | 2016 |
| Mcclements Construction Limited | Construction | 2018 |
| Mccormick Safe Plan Ltd | Professional & scientific | 2024 |
| Mcgarrity Tiling Contractors Ltd | Construction | 2023 |
| Mcgrady Financial Services Limited | Financial services | 1997 |
| Mcgrady Limited | Financial services | 1964 |
| Mcgraths Farm Shop Ltd | Wholesale & retail | 2024 |
| Mcgreevy Motors Ltd | Wholesale & retail | 2019 |
| Mckeown Rentals Ltd | Households | 2022 |
| Mckibbin Motors 2 Ltd | Wholesale & retail | 2012 |
| Mckibbin Motors Ltd | Wholesale & retail | 2006 |
| MCL Precision Engineering Ltd | Professional & scientific | 2026 |
| Mcmahon Commercial Cleaning Ltd | Administrative & support | 2023 |
| Mcmullan's Bar Ltd | Hospitality | 2021 |
| MCN Nail Ltd | Other services | 2024 |
| Mcnamee Freight Limited | Transport & logistics | 1998 |
| Mcpolin & Company Ltd | Professional & scientific | 2025 |
| Mcquoid Holdings Limited | Financial services | 2024 |
| MDK Advisory Ltd | Professional & scientific | 2015 |
| MED Bars Ltd | Hospitality | 2017 |
| Medi Packs Ltd | Wholesale & retail | 2021 |
| MEK Contracts Ltd | Construction | 2024 |
| Messana Investments Limited | Health & social care | 1988 |
| Methodical Media Ltd | Professional & scientific | 2018 |
| Methodsports Ltd | Other services | 2024 |
| Mews Events Ltd | Real estate | 2026 |