| Houserentni Ltd | Real estate | 2022 |
| Housing LMS Limited | Education | 2019 |
| Howard Abraham (Motors) Limited | Wholesale & retail | 1960 |
| HOY & Dorman Ltd | Professional & scientific | 2007 |
| HOY Dorman Group Limited | Extraterritorial | 2015 |
| Hoysmart Ltd | Administrative & support | 2022 |
| HPA Architecture Ltd | Professional & scientific | 2000 |
| HR Commerce Ltd | Wholesale & retail | 2024 |
| Htsni Ltd | Manufacturing | 2025 |
| Huhtamaki (Lurgan) Limited | Manufacturing | 1935 |
| Human Loves Robot Limited | Information & communication | 2021 |
| Humble BEE Therapies Ltd | Other services | 2023 |
| Hunters Chase Management Company Ltd | Real estate | 2013 |
| Hyco Developments Limited | Construction | 1984 |
| Hydebank Developments Limited | Real estate | 1999 |
| Hydra 3D Ltd | Professional & scientific | 2019 |
| Hylands Media Productions Ltd | Professional & scientific | 2017 |
| I & H Food Ltd | Hospitality | 2025 |
| I TAN Limited | Health & social care | 2017 |
| I.C.B. Emulsions Limited | Manufacturing | 1991 |
| IAJ Technologies Limited | Wholesale & retail | 2024 |
| IBS Systems (NI) Ltd | Wholesale & retail | 2002 |
| IGO Distribution Ltd | Wholesale & retail | 2022 |
| IGO Van Hire Limited | Administrative & support | 2024 |
| Ikmk Ltd | Professional & scientific | 2013 |
| Ilimitado Studio Ltd | Information & communication | 2024 |
| Ille Paper Service Limited | Wholesale & retail | 2006 |
| Imex Holdings Limited | Professional & scientific | 1992 |
| Imex Systems Limited | Professional & scientific | 1983 |
| Impact Performance & Conditioning Ltd | Arts & recreation | 2019 |
| IMR Automation Limited | Professional & scientific | 2013 |
| Inclusioniq Ltd | Administrative & support | 2021 |
| Incontrol Physiotherapy Limited | Health & social care | 2019 |
| Indian Tree Inc Ltd | Hospitality | 2015 |
| Indie and Willow Ltd | Wholesale & retail | 2022 |
| Indigo Van Hire Limited | Administrative & support | 2019 |
| Infallible Worship CIC | Other services | 2026 |
| Inner Harmony Limited | Extraterritorial | 2023 |
| Inspire ABM Care Limited | Health & social care | 2025 |
| Inspiringways Training and Consultancy Ltd | Education | 2019 |
| Integrated Timber Solutions Limited | Manufacturing | 2006 |
| Intergal Pharma Limited | Wholesale & retail | 2012 |
| Internet Marketing Studio Ltd | Professional & scientific | 2010 |
| Intouch Holdings Limited | Construction | 2002 |
| Intouch Network Solutions Ltd | Information & communication | 1996 |
| Inventbox Limited | Information & communication | 2026 |
| Invitio Limited | Information & communication | 2025 |
| Ipapa Ltd | Education | 2025 |
| Iphysio Clinics Ltd | Health & social care | 2025 |
| Ipsum Media Limited | Professional & scientific | 2020 |
| Irwin Engineering Group Limited | Manufacturing | 2002 |
| Irwin M&E Limited | Construction | 1999 |
| Irwin Properties Limited | Construction | 2016 |
| Irwins Sportsturf Limited | Wholesale & retail | 2018 |
| Island Energy Ltd | Energy | 2026 |
| Island Salads Ltd | Wholesale & retail | 2004 |
| Italia Restaurant Ltd | Hospitality | 2012 |
| Itssoome Limited | Wholesale & retail | 2016 |
| Ivan Megaw & SON Limited | Agriculture & fishing | 2019 |
| IVY and Willow Designs Ltd | Other services | 2023 |
| IZS Atelier Ltd | Wholesale & retail | 2026 |
| J & a Morrow Limited | Hospitality | 2000 |
| J Cailer Ltd | Health & social care | 2022 |
| J Dunn Electrical Limited | Construction | 2019 |
| J Facial Aesthetics Limited | Health & social care | 2022 |
| J H M Properties Limited | Real estate | 2015 |
| J M Concrete, Cutting & Drilling Ltd | Construction | 2024 |
| J Mcclimond Engineering Ltd | Manufacturing | 2010 |
| J P Mackle Ltd | Other services | 2022 |
| J T Fletcher Engineering Ltd | Manufacturing | 2025 |
| J W Stephenson Ltd | Construction | 2020 |
| J.A. Woodside & Co Limited | Construction | 1939 |
| J.D. Autos (N.I.) Ltd | Wholesale & retail | 2021 |
| J.D. Owen & Sons Limited | Construction | 1991 |
| J.J. Conlon & SON Limited | Construction | 2007 |
| J.J. Pierson Ltd | Wholesale & retail | 2005 |
| J2 Engineering Ltd | Manufacturing | 2020 |
| JAB Contracts Ltd | Construction | 2024 |
| Jacaa Property Group Ltd | Construction | 2025 |
| Jackson Andrews Consultants Limited | Administrative & support | 1985 |
| Jackson Andrews Trustees Limited | Administrative & support | 1985 |
| Jackson Reece Ltd | Manufacturing | 2003 |
| Jacobs Luxury BED Frames Ltd | Manufacturing | 2022 |
| JADM84 Payroll Services Ltd | Administrative & support | 2023 |
| JAH Translation Ltd | Professional & scientific | 2023 |
| Jajj Property Ltd | Real estate | 2021 |
| Jallen Enterprises Ltd | Hospitality | 2023 |
| James a. S. Finlay (Holdings) Limited | Financial services | 1978 |
| James a. S. Finlay Limited | Manufacturing | 1999 |
| James Conway Tattoos Ltd | Other services | 2023 |
| James E. Mccabe Limited | Wholesale & retail | 1975 |
| James Mccann & Sons Ltd | Wholesale & retail | 2005 |
| Janda Fore Trading Limited | Financial services | 2024 |
| Jans Jewellers Limited | Wholesale & retail | 2010 |
| Jasmin Gate Holdings Limited | Financial services | 2024 |
| Jasmine Health Limited | Wholesale & retail | 2009 |
| Jason Tandy Limited | Construction | 2022 |
| JAY Scissors Ltd | Other services | 2012 |
| JAZ Care Ltd | Health & social care | 2022 |
| Jazzlife Alliance 2024 Limited | Education | 2024 |