| Joint Independent Group for Study and Action Limited | Education | 1996 |
| Jojo's Fashion House Ltd | Wholesale & retail | 2024 |
| Jomo Properties Ltd | Real estate | 2022 |
| Jomur Ltd | Wholesale & retail | 2019 |
| Jonathan Downey Ltd | Wholesale & retail | 2022 |
| Jonathan MC Birney Ltd | Construction | 2016 |
| Jonathan MC Geough Haulage Ltd | Transport & logistics | 2019 |
| Jonesborough and Dromintee Community Enterprises Limited | Real estate | 1994 |
| Jonesborough Developments Ltd | Construction | 2025 |
| Jonesborough Glass Ltd | Construction | 2015 |
| Jonesborough Wholesale Ltd | Wholesale & retail | 2011 |
| Jonsel Enterprises Ltd | Wholesale & retail | 2001 |
| Joseph Brennan Bakeries NI Unlimited Company | Manufacturing | 2019 |
| Joseph Hughes Building Contractor Limited | Construction | 2015 |
| Joss Skelton Ltd | Wholesale & retail | 2024 |
| Jotco Limited | Real estate | 2025 |
| Journeysni C.I.C. | Transport & logistics | 2023 |
| Joyce's Distribution NI | Wholesale & retail | 2020 |
| JP & D Farms Ltd | Agriculture & fishing | 2024 |
| JP Devlin Media Ltd. | Manufacturing | 2011 |
| JPD Commercial Services Ltd | Professional & scientific | 2024 |
| Jphlaw Limited | Professional & scientific | 2015 |
| JPM Properties (NI) Limited | Hospitality | 2010 |
| Jpmp Plastering Limited | Construction | 2019 |
| JPS Safety Solutions Ltd | Public administration | 2022 |
| JR Electrical Services Ltd | Construction | 2017 |
| Jray Global Limited | Professional & scientific | 2023 |
| Jrdb N.I. Limited | Hospitality | 2024 |
| Jrex Ltd | Administrative & support | 2022 |
| Jrice Properties Ltd | Real estate | 2026 |
| Jrkc Construction Ltd | Construction | 2025 |
| Jrkc Ltd | Hospitality | 2025 |
| JRT Construction Services Ltd | Construction | 2026 |
| JS Marketing (N.I.) Limited | Wholesale & retail | 2000 |
| JSC Construction Consultants Limited | Professional & scientific | 2022 |
| JSC Contracts Ltd | Construction | 2024 |
| JSC Plastering Ltd | Construction | 2020 |
| JSK Concrete and Steel Fixing Ltd | Construction | 2021 |
| JSM Contracts Ltd | Construction | 2021 |
| JST Contracts IRE Limited | Transport & logistics | 2021 |
| JT Supplies (Newry) Ltd | Wholesale & retail | 2021 |
| JTL Cranes Ltd | Construction | 2026 |
| JTM Contracting Ltd | Construction | 2025 |
| JTS Construction & Demolition Ltd | Construction | 2019 |
| Juggle Group UK Ltd | Administrative & support | 2024 |
| Jumping Pillows Limited | Arts & recreation | 2016 |
| Just Good Grub Limited | Hospitality | 2017 |
| JV Kelly Ltd | Wholesale & retail | 2019 |
| JV Restaurants Ltd | Hospitality | 2021 |
| JWS Water Ltd | Manufacturing | 2025 |
| K & R Bricklaying Ltd | Construction | 2020 |
| K C Formwork Limited | Construction | 2014 |
| K Conlon Holdings Ltd | Real estate | 2022 |
| K&A Farms Ltd | Agriculture & fishing | 2026 |
| K&J Johnston Transport Ltd | Transport & logistics | 2025 |
| K&J Lennon Consultancy Ltd | Arts & recreation | 2025 |
| K-Dos Limited | Wholesale & retail | 2006 |
| K.P. Nets Limited | Agriculture & fishing | 2010 |
| K.S. Developments Limited | Construction | 1993 |
| K1 Property Ltd | Real estate | 2026 |
| K2 Fitness Limited | Other services | 2022 |
| K20 Holdings Limited | Real estate | 2025 |
| KA 21 Ltd | Hospitality | 2021 |
| Ka-Boom Technology Limited | Professional & scientific | 2024 |
| Kaizen Operations Ltd | Education | 2026 |
| Kameko Limited | Real estate | 2026 |
| Kandex Limited | Wholesale & retail | 2024 |
| Kane Global Bloodstock Limited | Agriculture & fishing | 2024 |
| Kansas Holdings Limited | Financial services | 2022 |
| Kanya Ltd | Hospitality | 2023 |
| Karl One Ltd | Real estate | 2026 |
| Karmagh Healthcare Ltd | Health & social care | 2019 |
| Karmon Property Limited | Real estate | 2017 |
| Karyda Consulting (N.I.) Limited | Professional & scientific | 2010 |
| KAS Farms Ltd | Agriculture & fishing | 2017 |
| Kateg Limited | Mining & quarrying | 2015 |
| Kavanagh Medical Limited | Health & social care | 2012 |
| Kavanagh Travel (NI) Ltd | Extraterritorial | 2009 |
| KAY Schoene Ltd | Wholesale & retail | 2024 |
| KB Engineering & Fabrication Ltd | Construction | 2016 |
| KB Estimating Ltd | Professional & scientific | 2020 |
| KB Lisburn Ltd | Arts & recreation | 2015 |
| KB Shaft Limited | Arts & recreation | 2015 |
| KBE Developments Ltd | Real estate | 2019 |
| KBE Stores Limited | Real estate | 2025 |
| Kbrt Trading Ltd | Wholesale & retail | 2016 |
| KC Hire & Sons Limited | Administrative & support | 2017 |
| KC Trading Ltd | Wholesale & retail | 2019 |
| Kcdm Property Ltd | Real estate | 2024 |
| KD Agri Ltd | Agriculture & fishing | 2025 |
| KD Remediation Limited | Water & waste | 2019 |
| Kean International Limited | Transport & logistics | 2025 |
| Keane Breathnach Limited | Professional & scientific | 2010 |
| Kearney Fishing Ltd | Agriculture & fishing | 2008 |
| Kearney Fitout UK Ltd | Construction | 2025 |
| Kearney Haulage Limited | Transport & logistics | 2015 |
| Kearns & Murtagh Limited | Wholesale & retail | 1996 |
| Keefreight Ltd | Transport & logistics | 2020 |
| Keegal Lodge Ltd | Real estate | 2025 |
| Keen Innovations Ltd | Wholesale & retail | 2024 |