| JMD Plant Hire Limited | Administrative & support | 2020 |
| JMD Properties Ltd | Construction | 2018 |
| JMG Joinery Ltd | Construction | 2025 |
| JMH Privacy Consultants Ltd | Professional & scientific | 2021 |
| JMK Transport Solutions Ltd | Transport & logistics | 2019 |
| JOE Toland Commercials U.K. Limited | Wholesale & retail | 2012 |
| John Cameron Limited | Administrative & support | 2018 |
| John M Coyle Paving Ltd | Construction | 2008 |
| John Porter Joinery & Construction Ltd | Construction | 2026 |
| John Quigley Construction NI Ltd | Construction | 2024 |
| Johnston Financial Solutions Limited | Financial services | 2013 |
| Johnstons' Caravans (NI) Limited | Wholesale & retail | 2020 |
| Joinery Workshop Services Ltd | Manufacturing | 2019 |
| Jordan Fitout Construction Guernsey Ltd | Construction | 2024 |
| Joseph Campbell & Company Limited | Professional & scientific | 2014 |
| Josh Mccorkell Plumbing and Heating Ltd | Construction | 2024 |
| Joule Group Holdings Limited | Professional & scientific | 2019 |
| JPC Furnishings Ltd | Construction | 2026 |
| JPM Aggregates Ireland Limited | Construction | 2005 |
| JR Designing Ltd | Professional & scientific | 2020 |
| JSA Enterprises Limited | Hospitality | 2016 |
| Jsdke Ltd | Real estate | 1999 |
| JSE Computing Limited | Information & communication | 1998 |
| Jtabc Projects Ltd | Real estate | 2022 |
| JTM Holdings Limited | Professional & scientific | 1983 |
| Jujac Limited | Real estate | 2018 |
| Just Feckin' Gifts Ltd | Wholesale & retail | 2021 |
| Just Vapour Limited | Wholesale & retail | 2022 |
| JW Electrics Ltd | Manufacturing | 2019 |
| JWD Commerce Ltd | Wholesale & retail | 2024 |
| K Bryson Construction Ltd | Construction | 2022 |
| K C Rally Service Ltd | Wholesale & retail | 2008 |
| K N Mcgowan Ltd | Construction | 2025 |
| K S Electrics (NI) Ltd | Construction | 2000 |
| K&R Mcgowan Ltd | Professional & scientific | 1971 |
| K-Doc Plant Ltd | Construction | 2022 |
| K.C. Storess Ltd | Wholesale & retail | 2003 |
| K.C.P.D Limited | Other services | 2023 |
| K2 Design Ltd | Professional & scientific | 2016 |
| K83 Convenience Ltd | Wholesale & retail | 2022 |
| K9 Lodge Ltd | Agriculture & fishing | 2021 |
| Kaed Holdings Limited | Real estate | 2024 |
| Kahn Johannes Ltd | Wholesale & retail | 2024 |
| Kaizen Leisure Limited | Wholesale & retail | 2023 |
| Kajora Investments Ltd | Real estate | 2023 |
| Kal-El Coffee Limited | Wholesale & retail | 2025 |
| Kamac Developments Ltd | Construction | 2026 |
| Karalbri Property Company Limited | Real estate | 2000 |
| KAT B Nails Ltd | Extraterritorial | 2023 |
| Katamaran Industries Ltd | Professional & scientific | 2024 |
| Katiss Zgseg Ltd | Wholesale & retail | 2024 |
| KB Kooling Limited | Manufacturing | 2022 |
| KBL E-Commerce Ltd | Wholesale & retail | 2023 |
| KC Flooring Consultancy Ltd | Professional & scientific | 2018 |
| KC Properties Derry Ltd | Real estate | 2026 |
| KCC Ceilings an Partitions Ltd | Construction | 2022 |
| KCC Interiors Ltd | Construction | 2018 |
| KD Properties (N.I.) Limited | Real estate | 2015 |
| KD Thornhill Taxis Limited | Transport & logistics | 2025 |
| Kdep Ltd | Wholesale & retail | 2007 |
| Kead Investments Limited | Real estate | 2017 |
| Kearney Law Group Ltd | Professional & scientific | 2019 |
| Kebroyde Limited | Hospitality | 2013 |
| KEE Real Estate Ltd | Households | 2017 |
| Keenan Haulage Limited | Transport & logistics | 2018 |
| Keeva Group Ltd | Wholesale & retail | 2025 |
| Keiran Baines Ltd | Professional & scientific | 2025 |
| Keishaeisha Limited | Health & social care | 2025 |
| Kelleher Serviced Accommodation Ltd | Real estate | 2023 |
| Keltik Solutions Limited | Real estate | 2018 |
| KEN Gibson (INT) Ltd | Information & communication | 2025 |
| KEN Mccorkell Tyre Service Ltd | Wholesale & retail | 2012 |
| Kenbar Limited | Real estate | 1986 |
| Kercon Construction Limited | Construction | 2003 |
| Kerry Eyre Cleaning Ltd | Other services | 2002 |
| Keturr Holdings Ltd | Financial services | 2025 |
| Kevin G.P. Kelly & Co. Ltd | Professional & scientific | 2020 |
| Kevin Gallagher Construction Ltd | Professional & scientific | 2022 |
| Kevin Watson Ltd | Financial services | 2016 |
| Kevmar Ltd | Construction | 2013 |
| Key Asset Developments Limited | Construction | 2025 |
| Key Asset Properties Ltd | Real estate | 2024 |
| Keystone Consulting & Digital Solutions Ltd | Information & communication | 2026 |
| Keystone Investments (N.I) Limited | Construction | 2016 |
| KF Contracts Ltd | Manufacturing | 2019 |
| KF Industries Ltd | Wholesale & retail | 2011 |
| KGM NI Properties Ltd | Real estate | 2025 |
| KGT Services Limited | Construction | 2019 |
| KH Furniture Ltd | Wholesale & retail | 2026 |
| KHG Digital Ltd | Information & communication | 2025 |
| Kick-On Coaching CIC | Arts & recreation | 2025 |
| Kids Health Consulting Limited | Health & social care | 2024 |
| Kidz Playtime C.I.C. | Other services | 2018 |
| Kilcreen Consulting Limited | Construction | 2021 |
| Kilcreen Contracts Limited | Construction | 2024 |
| Kilcreen Property Limited | Real estate | 2024 |
| Kildare Projects Ltd | Real estate | 2021 |
| Kilgore Transport Limited | Transport & logistics | 2016 |
| Killerfaith Ltd | Construction | 2025 |
| Kimbles Outside Catering Ltd | Hospitality | 2026 |