| JH Tyres Limited | Wholesale & retail | 2007 |
| JH Veterinary Limited | Professional & scientific | 2026 |
| Jigsaw Financial Associates Limited | Financial services | 2009 |
| Jireh Ministries Ltd | Other services | 2013 |
| JJC NI Consultancy Ltd | Financial services | 2011 |
| JJF Validation Solutions Ltd | Professional & scientific | 2025 |
| JJG Homes Limited | Construction | 2022 |
| JJW Farms Ltd | Agriculture & fishing | 2017 |
| Jlim Investments Ltd | Real estate | 2019 |
| JLJ Mechanical Services Ltd | Construction | 2025 |
| JM Allen Construction Ltd | Construction | 2025 |
| Jmac Contracts Ltd | Construction | 2017 |
| JMC Consultancy Services Ltd | Professional & scientific | 2020 |
| Jmcc Enterprises Ltd | Wholesale & retail | 2017 |
| Jmcit Ltd | Information & communication | 2015 |
| Jmcp Engineering Limited | Professional & scientific | 2023 |
| JMP Agencies Limited | Construction | 2012 |
| JMW Farms Ltd | Agriculture & fishing | 2005 |
| JOE FOX Contracts Limited | Construction | 2007 |
| JOH Contracts Ltd | Construction | 2018 |
| John Cathcart and Sons, Limited | Construction | 1957 |
| John Smyth Bookmakers Limited | Arts & recreation | 2024 |
| Johnston Advisors Limited | Professional & scientific | 2009 |
| Johnstons Bakery Ltd | Manufacturing | 2010 |
| Jome Developments Ltd | Construction | 2006 |
| Joseph a. Linton & SON Limited | Wholesale & retail | 1955 |
| JPM Motors Ltd | Wholesale & retail | 2021 |
| Jpma Ltd | Professional & scientific | 2026 |
| JPS Armagh Ltd | Hospitality | 2016 |
| JRW1 | Real estate | 2015 |
| JRW2 Limited | Wholesale & retail | 2021 |
| JS Livestock Limited | Agriculture & fishing | 2021 |
| JS Wilson Ltd | Real estate | 2024 |
| JWR Media Limited | Arts & recreation | 2019 |
| K & D Enterprises Limited | Real estate | 2004 |
| K P D (Developments) Limited | Real estate | 2000 |
| K Two Machinery Limited | Manufacturing | 2024 |
| K-Lite Electrical Limited | Construction | 2014 |
| KA Associates Limited | Professional & scientific | 2013 |
| Kalymnos Fuel Engineering Ltd | Wholesale & retail | 2013 |
| KAM Cooling Ltd | Professional & scientific | 2021 |
| Karmagh Limited | Other services | 2017 |
| Katerina 2014 Ltd | Wholesale & retail | 2018 |
| Kaypart Ltd | Manufacturing | 2021 |
| KB Haulage Ltd | Transport & logistics | 2024 |
| Kbpainting Limited | Construction | 2025 |
| KBS Contracts (NI) Ltd | Construction | 2013 |
| KC Joinery (N.I.) Limited | Construction | 2021 |
| KC Utilities Ltd | Manufacturing | 2014 |
| KCS Property Holdings Ltd | Financial services | 2024 |
| KDR Automation Ltd | Information & communication | 2023 |
| KEE Grains Ltd | Wholesale & retail | 2025 |
| Keegans Bar Limited | Hospitality | 2015 |
| Keenan & Co Construction Ltd | Agriculture & fishing | 2019 |
| Keenan Enterprises Ltd | Professional & scientific | 2011 |
| Keith Dougan Mobile Tyre Services Ltd | Manufacturing | 2021 |
| Kelly Real Estate Ltd | Real estate | 2025 |
| Kelly Recycling (NI) Limited | Construction | 2025 |
| Kempton Law Limited | Professional & scientific | 2020 |
| Kendal Construction Ltd | Wholesale & retail | 2022 |
| Kennedy Residential Ltd | Real estate | 2022 |
| Kernan Capital Limited | Financial services | 2021 |
| Kernan Financial Limited | Professional & scientific | 2018 |
| Kernan Transport Ltd | Transport & logistics | 2019 |
| Keydropgiveaways Ltd | Arts & recreation | 2025 |
| Keys Killylea Ltd | Education | 2022 |
| KG Haulage Ltd | Transport & logistics | 2019 |
| KGB Poultry Ltd | Agriculture & fishing | 2015 |
| KGF Holdings Ltd | Financial services | 2025 |
| KGK Haulage Ltd | Transport & logistics | 2025 |
| KHC Limited | Wholesale & retail | 2004 |
| Kiercon Consultancy Limited | Construction | 2013 |
| Kilbracks Consultancy Limited | Administrative & support | 2019 |
| Kilbracks Engineering Limited | Construction | 2004 |
| Kilbracks Farm Ltd | Agriculture & fishing | 2015 |
| Kilcreevy Electrical Ltd | Construction | 2020 |
| Killeen Farms Limited | Agriculture & fishing | 2026 |
| Killuney Holdings Ltd | Construction | 2023 |
| Killyfaddy Contracts Ltd | Manufacturing | 2023 |
| Killymaddy Rural Development Group Ltd | Education | 2025 |
| Kilmacanty Transport Ltd | Transport & logistics | 2023 |
| Kilmore Services Limited | Professional & scientific | 2017 |
| Kineely Ltd | Construction | 2023 |
| Kinetic Power Solutions Ltd | Energy | 2025 |
| King Bros Quarry Ltd | Mining & quarrying | 2016 |
| Kingsbury Farm Enterprises Ltd | Wholesale & retail | 2025 |
| Kitchen Comps Ltd | Manufacturing | 2025 |
| KK Physiotherapy Limited | Health & social care | 2014 |
| KLX Transport Limited | Transport & logistics | 2019 |
| KM Tarmac Limited | Extraterritorial | 2015 |
| KMF Developments Ltd | Construction | 2021 |
| KMJ Contracts Ltd | Construction | 2023 |
| KMK Beauty, Aesthetics & Laser Ltd | Other services | 2021 |
| Knappagh Renewables Ltd | Energy | 2020 |
| Knipe Recruitment Limited | Administrative & support | 2014 |
| Konfloor Ltd | Construction | 2005 |
| Konnected ETS Ltd | Construction | 2024 |
| Konstruct Capital Limited | Financial services | 2026 |
| Konstruct Contracts Ltd | Construction | 2014 |
| Konstruct Group Limited | Construction | 2021 |