| Influenced by Penelope Limited | Professional & scientific | 2024 |
| Infurious Ltd | Information & communication | 2006 |
| Insight Business Solutions Ltd | Professional & scientific | 2010 |
| Inspecvision Limited | Manufacturing | 2003 |
| Inspired Memories Limited | Hospitality | 2025 |
| Inspirus Sports (Dubai) Limited | Arts & recreation | 2020 |
| Integritas Consulting & Training Ltd | Professional & scientific | 2021 |
| Integrity Property Services & Management Ltd | Real estate | 2020 |
| Interactive (Ireland) Limited | Wholesale & retail | 2002 |
| International Divine Democratic Rights Organisation (Iddro) Limited | Health & social care | 2025 |
| International Fighting Championships Ltd | Arts & recreation | 2019 |
| Inventevent Limited | Administrative & support | 2024 |
| Invincible Batteries Ltd | Wholesale & retail | 2024 |
| Ionic Talent Solutions Ltd | Administrative & support | 2019 |
| Iora Ltd | Administrative & support | 2025 |
| Ipark Glasgow Ltd | Transport & logistics | 2019 |
| Iphone Bits Limited | Information & communication | 2016 |
| Iprint 1925 Ltd | Manufacturing | 2023 |
| Irish Desi Weddings Ltd | Wholesale & retail | 2025 |
| Irish Soup Productions Limited | Information & communication | 2015 |
| IT Refreshed Global Limited | Wholesale & retail | 2015 |
| IT Support Belfast Ltd | Wholesale & retail | 2021 |
| Itouchenergy Limited | Manufacturing | 2012 |
| IVY Lane Ltd | Real estate | 2021 |
| J & B Practical Electrics Ltd | Information & communication | 2015 |
| J & F Trucks & Vans Limited | Wholesale & retail | 2015 |
| J & F Walsh Property Limited | Real estate | 2019 |
| J&Cm Ltd | Financial services | 2021 |
| J'S Retail Services Limited | Wholesale & retail | 2015 |
| J. D. Hunter & Co. Limited | Wholesale & retail | 1998 |
| J.D. Fork Trucks Limited | Wholesale & retail | 1977 |
| J.G. Burns Limited | Manufacturing | 1978 |
| J.Mckee Commercials Ltd | Manufacturing | 2025 |
| Jackson & Co Clothing Limited | Wholesale & retail | 2023 |
| Jacobson Modulars Ltd | Manufacturing | 2024 |
| Jake Harvey Investments Ltd | Real estate | 2025 |
| James Boyd & Sons (Carnmoney) Limited | Mining & quarrying | 1934 |
| James Gault International Horse Transport Ltd | Transport & logistics | 2021 |
| James P Corey Transport Ltd | Transport & logistics | 2016 |
| Jamie-Qs-Solutions Ltd | Professional & scientific | 2025 |
| Jando Media 2003 Limited | Information & communication | 2026 |
| Jane Erwin Aesthetics Ltd | Other services | 2022 |
| Jazign Limited | Professional & scientific | 2024 |
| JB Performers Ltd | Arts & recreation | 2021 |
| JDC Apex Properties Ltd | Households | 2025 |
| Jenarron Therapeutics Limited | Manufacturing | 2012 |
| Jenback Properties Limited | Construction | 2020 |
| Jengana Association Limited | Health & social care | 2013 |
| Jennings Limited | Manufacturing | 1990 |
| JER Enterprises (NI) Ltd | Manufacturing | 2014 |
| JER Property Ltd | Real estate | 2023 |
| Jet-L Consulting Limited | Information & communication | 2016 |
| JG NI Aesthetics Ltd | Other services | 2026 |
| JH Site Maintenance Ltd | Administrative & support | 2026 |
| JHS PVT Ltd | Hospitality | 2025 |
| JIM Consultancy Ltd | Professional & scientific | 2023 |
| JJE Sales Ltd | Wholesale & retail | 2024 |
| JLA Construction Ltd | | 2006 |
| JM E-Commerce Ltd | Wholesale & retail | 2023 |
| JMC Car & Commercial Repairs Ltd | Wholesale & retail | 2018 |
| JMC Transfers & Tours Limited | Transport & logistics | 2025 |
| Jmcg Property Rentals Ltd | Real estate | 2025 |
| JML Fire and Security Limited | Administrative & support | 2025 |
| JMR Fleet Training Ltd | Education | 2023 |
| JOD Consultants Ltd | Administrative & support | 2019 |
| JOE Kennedy Coaching Ltd | Education | 2024 |
| John Compton Limited | Agriculture & fishing | 1918 |
| John Haughey Rental Limited | Real estate | 2020 |
| John Henderson (Mallusk) Limited | Real estate | 2003 |
| John Morris Arboricultural Consultancy Ltd | Administrative & support | 2020 |
| JOHNS365SOLUTIONS Ltd | Information & communication | 2025 |
| Johnston Prams & Buggies Limited | Wholesale & retail | 1996 |
| Joinher Network CIC | Professional & scientific | 2019 |
| Jomac Sales Limited | Wholesale & retail | 2026 |
| Jonahs Vapes and Treats Ltd | Wholesale & retail | 2026 |
| Jordan Fleet Limited | Administrative & support | 2016 |
| Jordanstown Christian Centre Ltd | Other services | 2021 |
| Jordanstown Road Apartment Management Company Limited | Real estate | 2019 |
| JP NI Property Maintenance Ltd | Construction | 2025 |
| JPF Group Ltd | Hospitality | 2020 |
| Jpmni Ltd | Other services | 2020 |
| Jpmwork Limited | Construction | 2026 |
| JR Fleet Solutions Ltd | Administrative & support | 2023 |
| Jrcom Media Ltd | Information & communication | 2022 |
| JRM Renewables Ltd | Construction | 2022 |
| JSE Joinery Ltd | Construction | 2026 |
| JST NI Holdings Limited | Financial services | 2025 |
| JSW Landscapes Ltd | Administrative & support | 2026 |
| JTY Restaurants Limited | Wholesale & retail | 2007 |
| Juniors Fish & Chips Ltd | Hospitality | 2020 |
| JWY Foods Ltd | Hospitality | 2025 |
| JX2E Productions Ltd | Information & communication | 2025 |
| K H Mews Management Company Limited | Households | 2021 |
| K&E Aviation Ltd | Professional & scientific | 2023 |
| K11 Property Solutions Ltd | Real estate | 2019 |
| K2 Scaffolding (NI) LLP | | 2010 |
| K3 Ventures Ltd. | Information & communication | 2024 |
| Kafd Events Ltd | Financial services | 2020 |
| Kanit Consulting Limited | Information & communication | 2019 |
| Kariyil Limited | Health & social care | 2019 |