| Human Thrive Coaching Ltd | Health & social care | 2025 |
| Hunters Hill Holdings Ltd | Construction | 2019 |
| HY 2000 Ltd | Hospitality | 2025 |
| Hyrocks Hybrid Ltd | Arts & recreation | 2025 |
| IAM Scouting & Management LP | | 2018 |
| IAN Black Consulting Limited | Construction | 2003 |
| IBA - International Business Advisors LLP | | 2021 |
| IBE - International Business Experts Limited | Professional & scientific | 2023 |
| IC Property Ventures Ltd | Real estate | 2025 |
| Icon Consultors Limited | Professional & scientific | 2020 |
| Icon Creative Limited | Professional & scientific | 2002 |
| Iconiq Property Ltd | Real estate | 2025 |
| Ideal Credit Solutions (NI) Ltd | Construction | 2014 |
| Ideal Credit Solutions Ltd | Construction | 2014 |
| IES - International Executive Services Limited | Professional & scientific | 2024 |
| IF Intech Financial LLP | | 2017 |
| IFD Interiors Ltd | Financial services | 2015 |
| Ignite IT Ltd | Other services | 2010 |
| IK Engineering Ltd | Professional & scientific | 2018 |
| Ilmc Investments Limited | Financial services | 2018 |
| Ilumiware LP | | 2025 |
| IM Media Services Limited | Professional & scientific | 2020 |
| Imoveni Limited | Real estate | 2016 |
| Impact Conveyor Parts Limited | Wholesale & retail | 1997 |
| Impact Plumbing and Heating Ltd | Construction | 2026 |
| IN Tune Financial Limited | Financial services | 2022 |
| Incartus Developments Ltd | Construction | 2013 |
| Incredible Computers Limited | Manufacturing | 2015 |
| Indian Carick Limited | Real estate | 2016 |
| Indian Glengormley Ltd | Hospitality | 2014 |
| Indian Holywood Limited | Hospitality | 2013 |
| Indian Ocean NI Limited | Hospitality | 2003 |
| Indiquip Ltd | Energy | 2024 |
| Industrial Research & Technology Limited | Professional & scientific | 2006 |
| Infinite Store Ltd | Wholesale & retail | 2026 |
| Infinitemind Technologies Ltd | Information & communication | 2023 |
| INFINITY21 Ltd | Information & communication | 2021 |
| Init Build Ltd | Construction | 2008 |
| Inkspirational Branding Ltd | Manufacturing | 2024 |
| Innovate AI Ltd | Information & communication | 2023 |
| Innovative Development Group LLP | | 2021 |
| Innovegic Ltd | Wholesale & retail | 2016 |
| Insightquay Tech Ltd | Wholesale & retail | 2023 |
| Insightt Limited | Professional & scientific | 2017 |
| Inspecturgadget Ltd | Other services | 2021 |
| Inspired Education Centre Ltd | Education | 2025 |
| Instantor Limited | Extraterritorial | 2024 |
| Insurance Services (NI) Limited | Financial services | 2000 |
| Integrity Tyres Ltd | Wholesale & retail | 2013 |
| Intercontinental Business Associates Limited | Professional & scientific | 2020 |
| International Business Technologies LLP | | 2022 |
| International Capital Advisors Limited | Professional & scientific | 2025 |
| International Real Estate Franchise LP | | 2025 |
| International Taam Padideh Parsi Ltd | Wholesale & retail | 2023 |
| Interserve Ireland | Other services | 1996 |
| Into Light Tattoo Limited | Other services | 2023 |
| Investway Ltd | Wholesale & retail | 2007 |
| Ionad NA Fuiseoige Teoranta | Administrative & support | 2013 |
| Ionic Products Ltd | Manufacturing | 2019 |
| IOT Tech Limited | Professional & scientific | 2012 |
| Ipce Limited | Manufacturing | 1982 |
| Iphix Group Ltd | Other services | 2019 |
| Ipower Flexible Energy Ltd | Energy | 2009 |
| Irisarlene Limited | Hospitality | 2020 |
| Irish Bearings and Transmissions Limited | Extraterritorial | 1967 |
| Irish Door Systems (N.I.) Limited | Manufacturing | 2024 |
| Irish Whiskey Company Limited - the | Manufacturing | 1989 |
| Irwin Plumbing & Heating Limited | Construction | 2015 |
| IS What IT IS Ltd | Hospitality | 2025 |
| Island Productions Ltd | Information & communication | 1996 |
| It's Worth a Punt Ltd | Arts & recreation | 2023 |
| Itech Software Solutions Limited | Information & communication | 2024 |
| IVA Watch Limited | Information & communication | 2012 |
| Ivanka Miteva Limited | Other services | 2013 |
| Ivory Apartments Limited | Real estate | 2017 |
| Ivvar LP | | 2023 |
| IVY Sales LP | | 2018 |
| Iwap Inc Ltd | Arts & recreation | 2025 |
| J & L Gardening Services (2023) Ltd | Administrative & support | 2023 |
| J & M Mccullough Engineering Services Ltd | Professional & scientific | 2017 |
| J & P Pubs (Moira) Ltd | Hospitality | 2022 |
| J & P Pubs Holding Co Ltd | Financial services | 2023 |
| J Burns Holdings Ltd | Financial services | 2022 |
| J C Estate Agents Ltd | Professional & scientific | 2025 |
| J Compton Consultants Limited | Professional & scientific | 2014 |
| J Elliott Services Limited | Wholesale & retail | 2020 |
| J Farrell Joinery Limited | Construction | 2024 |
| J Gilmore Ltd | Manufacturing | 2025 |
| J J Shannon Ltd | Wholesale & retail | 2015 |
| J K H Consulting Limited | Construction | 2004 |
| J T Joinery Works Ltd | Construction | 2017 |
| J T Sheds & Joinery Ltd | Construction | 2017 |
| J W Motors Ltd | Wholesale & retail | 2011 |
| J&L Complete Solutions Ltd | Administrative & support | 2021 |
| J-Way Transport & Storage Limited | Transport & logistics | 2019 |
| J. Garrity Letting Ltd | Real estate | 2026 |
| J.& M. Trust Limited- the | Professional & scientific | 1972 |
| J.H. Irwin & SON (Fuels) Limited | Wholesale & retail | 1981 |
| J.L.G. Barnsoul Limited | Hospitality | 2024 |
| J.M.C. Restaurants Limited | Hospitality | 1993 |