| J a P (Sutton) Limited | Real estate | 2003 |
| J and J Driving School Limited | Education | 2024 |
| J Blain Properties Ltd | Real estate | 2025 |
| J C Crawford & Co Ltd | Professional & scientific | 2024 |
| J Corkey Limited | Health & social care | 2023 |
| J Crawford Aviation (NI) Ltd | Manufacturing | 2020 |
| J F Carberry & Co Limited | Financial services | 2022 |
| J Faloon Fitness & Boxing Limited | Arts & recreation | 2026 |
| J Fulton & Co LLP | | 2009 |
| J G Mccann and Company Solicitors Limited | Professional & scientific | 2024 |
| J H Carey IRL Ltd | Construction | 2025 |
| J H Carey Ltd | Construction | 2025 |
| J H Consultancies Ltd | Professional & scientific | 2022 |
| J Hospitality Ltd | Hospitality | 2025 |
| J HOY & Son's Ltd | Professional & scientific | 2023 |
| J HOY Aero Ltd | Manufacturing | 2026 |
| J K Developments (N.I.) Limited | Real estate | 1973 |
| J K Mediterranean Restaurant Ltd | Hospitality | 2025 |
| J L Armstrong & Sons Ltd | Construction | 2026 |
| J M Security N.I. Ltd | Administrative & support | 2024 |
| J Mainwaring Limited | Professional & scientific | 2024 |
| J MC Crudden Ltd | Wholesale & retail | 2020 |
| J Mccollum Property Holdings Ltd | Real estate | 2024 |
| J Mccourt & SON Ltd | Mining & quarrying | 2019 |
| J Mccrarren Ltd | Other services | 2025 |
| J Mcgennity Limited | Health & social care | 2025 |
| J Mcginnity Ltd | Real estate | 2019 |
| J Mclernon Consulting Ltd | Information & communication | 2024 |
| J Morrison Education Ltd | Other services | 2022 |
| J P Contracts (2023) Ltd | Construction | 2023 |
| J P Cope Surveying Ltd | Professional & scientific | 2018 |
| J P Grab Services Ltd | Water & waste | 2022 |
| J P Holdings (N.I.) Ltd | Construction | 2010 |
| J Sea Fishing Ltd | Agriculture & fishing | 2017 |
| J&C Entertainment Ltd | Administrative & support | 2024 |
| J&D Event Production Services Limited | Arts & recreation | 2025 |
| J&E International Investment Solutions Ltd | Construction | 2014 |
| J&G Community Services Ltd | Health & social care | 2025 |
| J&H Business Park Ltd | Real estate | 2025 |
| J&L Foods Ltd | Hospitality | 2024 |
| J&L Formwork Ltd | Construction | 2021 |
| J&M (N.I.) Ltd | Financial services | 2017 |
| J&Md Property Development Limited | Construction | 2016 |
| J&Md Property Services Ltd | Real estate | 2010 |
| J&P Medical Ltd | Health & social care | 2025 |
| J&S Decor Limited | Construction | 2018 |
| J&W Novelty Toys and Bucket Hats Ltd | Wholesale & retail | 2026 |
| J'S Lace Ltd | Wholesale & retail | 2026 |
| J-Ports UK Ltd | Wholesale & retail | 2025 |
| J. & J. Hunter Limited | Wholesale & retail | 1924 |
| J. & T. Plant Limited | Extraterritorial | 2011 |
| J. Ballantine Surfacing Ltd | Construction | 2011 |
| J. Cairns, Limited | Real estate | 1949 |
| J. J. Mcwilliams Property Ltd | Real estate | 2021 |
| J.& J.Haslett Limited | Extraterritorial | 1903 |
| J.A. Trading Limited | Professional & scientific | 1975 |
| J.A.M Building & Joinery Ltd | Manufacturing | 2019 |
| J.A.M. Developments Limited | Real estate | 1994 |
| J.A.M. Restaurants (2015) Ltd | Hospitality | 2015 |
| J.B. Plant Hire (Dungannon) Limited | Administrative & support | 1991 |
| J.B. Plant Hire Limited | Administrative & support | 1991 |
| J.B.G. Utilities Limited | Construction | 2018 |
| J.C. Patterson (Lisburn) Limited | Real estate | 1948 |
| J.C.Print Limited | Information & communication | 1979 |
| J.D. Mcgeown Limited | Construction | 1980 |
| J.E.K.M Properties Ltd | Hospitality | 2025 |
| J.E.Taylor (N.I.) Limited | Financial services | 1991 |
| J.H. Financial Planning Ltd | Financial services | 2007 |
| J.H.C. Hardware Holdings Limited | Financial services | 2024 |
| J.K. Lettings (Belfast) Ltd | Real estate | 2022 |
| J.M.C. Mechanical & Construction Ltd | Construction | 2004 |
| J.Morgan & Sons (Mayobridge) Limited | Mining & quarrying | 1966 |
| J.O.E. Hudson Limited | Health & social care | 2019 |
| J.P. Developments Limited | Construction | 1978 |
| J.P.D.M Hughes Limited | Extraterritorial | 2011 |
| J.P.L Invts Ltd | Real estate | 2010 |
| J.Rainey & Company Limited | Wholesale & retail | 1974 |
| J.S.M.K. (Management) Limited | Real estate | 1996 |
| J.T. Glover, Limited | Extraterritorial | 1938 |
| J.W. Gray Limited | Wholesale & retail | 1947 |
| J14R Holdings Limited | Financial services | 2024 |
| J2 Flooring Ireland Limited | Construction | 2025 |
| J23M LLP | | 2015 |
| J2L Consulting Ltd | Information & communication | 2018 |
| J3R Properties Ltd | Construction | 2026 |
| J5F Coaching Limited | Education | 2023 |
| JA Couriers Belfast Ltd | Transport & logistics | 2020 |
| JA Holdings Belfast Ltd | Financial services | 2025 |
| JA Investments One Limited | Hospitality | 2018 |
| JA Medical Ltd | Health & social care | 2021 |
| JA Property Belfast Ltd | Real estate | 2025 |
| JA Suprise Limited | Wholesale & retail | 2024 |
| JAA Receivables Limited | Transport & logistics | 2018 |
| Jaap Belfast Limited | Other services | 2025 |
| Jaap Forest Limited | Other services | 2019 |
| Jaap Juice Bar Limited | Wholesale & retail | 2025 |
| Jaap Lagan Limited | Other services | 2019 |
| JAB Accountancy Ltd | Administrative & support | 2016 |
| JAB Power Ltd | Energy | 2016 |
| Jabbari Holdings Ltd | Financial services | 2025 |