| Irradiance Energy Ltd | Administrative & support | 2017 |
| Irwin Agri Ltd | Wholesale & retail | 2024 |
| Irwin Farm Supplies Ltd | Wholesale & retail | 2003 |
| Irwins Quality Aggregates Limited | Mining & quarrying | 2012 |
| Island Property Developments Ltd | Real estate | 2006 |
| ISM Robotics Ltd | Manufacturing | 2014 |
| Isms Independent Specialist Maintenance Services Ltd | Manufacturing | 2021 |
| Ispini Charcuterie Ltd | Manufacturing | 2019 |
| ISS (Engineering) Limited | Manufacturing | 2010 |
| IT Stack Systems Ltd | Information & communication | 2024 |
| Itech-Church Media Ltd | Information & communication | 2018 |
| Ivanov Combined Services (ICS) Ltd | Water & waste | 2024 |
| Ivapewholesale(Ni) Ltd | Wholesale & retail | 2024 |
| Ivory Pavilion Ltd | Administrative & support | 2016 |
| J & a Construction (NI) Ltd | Construction | 2003 |
| J & a Developments Ltd | Construction | 1994 |
| J & B Contracts Limited | Construction | 2017 |
| J & E 8 Ltd | Hospitality | 2013 |
| J & H Group Ltd | Financial services | 2019 |
| J & J NI Holdings Limited | Financial services | 2017 |
| J a P (Staines) Limited | Real estate | 2002 |
| J B Bentley & Sons Ltd | Construction | 2014 |
| J F Exchange Limited | Administrative & support | 2019 |
| J G Plant Sales & Hire Ltd | Administrative & support | 2021 |
| J Hughes Accountants Limited | Professional & scientific | 2025 |
| J Maxwell & SON Trailer Services Ltd | Manufacturing | 2026 |
| J-Bet Limited | Financial services | 2024 |
| J-Jet Capital Limited | Real estate | 2024 |
| J. Stockdale and SON Ltd | Transport & logistics | 2000 |
| J.F. Andrews Engineering Limited | Manufacturing | 1973 |
| J.J. Kelly & Co. Accountants Ltd | Professional & scientific | 2001 |
| J.J. Quinn & Co (Electrical) Ltd | Wholesale & retail | 2005 |
| J.K. Car Sales NI Ltd | Wholesale & retail | 2022 |
| J.K. Genetics Ltd | Agriculture & fishing | 2018 |
| J.M.B. Coaches Ltd | Transport & logistics | 2005 |
| Jabez Limited | Real estate | 2025 |
| Jack Coulter Ltd | Arts & recreation | 2021 |
| Jacx Holdings Limited | Financial services | 2025 |
| Jacx Properties Limited | Real estate | 2025 |
| Jada Kerr Ltd | Construction | 2025 |
| Jaffs Coaches Ltd | Transport & logistics | 2015 |
| JAM Sandwich Productions Limited | Information & communication | 2021 |
| James Casey & Co Ltd | Professional & scientific | 2023 |
| James Mackle Limited | Manufacturing | 1986 |
| James Taggart Ltd | Other services | 2013 |
| Jamm Utilities Ltd | Construction | 2012 |
| JAP (Moygashel) LLP | | 2006 |
| Jardin Trading N.I. Limited | Wholesale & retail | 2021 |
| Jardine Tree Surgery Limited | Administrative & support | 2012 |
| JAS Furnishings Ltd | Wholesale & retail | 2020 |
| JAS Properties Limited | Construction | 1999 |
| JAS Trading Ltd | Wholesale & retail | 2023 |
| Jask Developments Limited | Construction | 2017 |
| Jasmine Enterprises Limited | Professional & scientific | 2019 |
| JB Engineering Supplies Limited | Manufacturing | 2006 |
| JBL Heating & Plumbing Ltd | Construction | 2024 |
| JC Contracts Ltd | Agriculture & fishing | 2025 |
| JCC Corporate Holdings Ltd | Financial services | 2024 |
| JCE Johnston Property Ltd | Real estate | 2024 |
| Jdfp Property Ltd | Real estate | 2021 |
| Jdpt Ltd | Hospitality | 2017 |
| JDQ Contract Services Ltd | Construction | 2016 |
| JE Wind Ltd | Manufacturing | 2015 |
| Jeanie Properties Ltd | Real estate | 2013 |
| JEC Group Ltd | Financial services | 2001 |
| Jemmko Holdings Ltd | Financial services | 2024 |
| Jemmko Trading Ltd | Wholesale & retail | 2024 |
| Jeremy Hobson Limited | Agriculture & fishing | 2003 |
| JFK Electrical (NI) Ltd | Wholesale & retail | 2014 |
| JFT Developments Ltd | Construction | 2019 |
| JG Building Contracts Ltd | Construction | 2022 |
| JGQ (NO. 1) Limited | Construction | 2014 |
| JGQ (NO. 2) Limited | Construction | 2014 |
| JGQ (NO. 3) Limited | Real estate | 2014 |
| JGQ Limited | Construction | 2014 |
| JHK Wholesale Ltd | Wholesale & retail | 2024 |
| Jianice Ltd | Wholesale & retail | 2024 |
| Jimmy's MOY Limited | Hospitality | 2017 |
| JJP Property Investments Limited | Real estate | 2018 |
| JJQ Trading Ltd | Wholesale & retail | 2012 |
| Jmac Safety Consultants Ltd | Administrative & support | 2023 |
| JMC Fabrications Ltd | Extraterritorial | 2003 |
| JMC Rentals Limited | Real estate | 2013 |
| JMK Company Holding Ltd | Financial services | 2021 |
| JMK Electrics Ltd | Manufacturing | 2010 |
| JMK Investments Limited | Financial services | 2021 |
| JNA Ltd | Transport & logistics | 2023 |
| JOE Foley Limited | Professional & scientific | 2014 |
| JOE MÓR Electrical Ltd | Manufacturing | 2017 |
| JOE Weir Engineering Ltd | Construction | 2007 |
| John HOY SON & Murphy Limited | Professional & scientific | 2011 |
| John Mullan Contracts Ltd | Construction | 2016 |
| John Paul Mchugh Ltd | Information & communication | 2015 |
| John Stevenson & Co Limited | Real estate | 1887 |
| Johnston Poultry Sales Limited | Agriculture & fishing | 2011 |
| Jollys Promotion Ltd | Arts & recreation | 2012 |
| Jordan International Holdings Limited | Professional & scientific | 2019 |
| Jordan International Property Limited | Real estate | 2019 |
| Jordan International Transport Ltd | Transport & logistics | 2009 |
| Jordan Services Limited | Construction | 2002 |