| John Mcdowell (Newtownards Road) Limited | Health & social care | 2021 |
| John Mcerlean Limited | Hospitality | 2005 |
| John Mcgahey & SON Unlimited | Transport & logistics | 1975 |
| John Mcgarry Ltd | Wholesale & retail | 2025 |
| John Mchugh Ltd | Wholesale & retail | 2025 |
| John Mckee (NI) Limited | Professional & scientific | 2023 |
| John Miller (NI) Ltd | Professional & scientific | 2002 |
| John Moane Ltd | Manufacturing | 2021 |
| John Moorehead Limited | Health & social care | 2012 |
| John Morgan & Sons Limited | Transport & logistics | 1955 |
| John Morgan Holdings Limited | Professional & scientific | 2003 |
| John Mullen Ltd | Wholesale & retail | 2025 |
| John Noble Electrics Limited | Construction | 2016 |
| John Robinson Ltd | Wholesale & retail | 2003 |
| John Russell Bricklaying Ltd | Construction | 2018 |
| John Smyth's Estates Limited | Real estate | 1954 |
| John Street Lane Mews (Newtownards) Management Limited | Extraterritorial | 2005 |
| John Warnock Ltd | Wholesale & retail | 2025 |
| John Yeats Estates Limited | Real estate | 1955 |
| John's Square Management Company Limited | Households | 2004 |
| Johncorp (NO.2) Limited | Real estate | 2014 |
| Johncorp (NO.3) Limited | Real estate | 2014 |
| Johnson Integrated Services Ltd | Health & social care | 2018 |
| Johnson Stevens (N.I.) Limited | Transport & logistics | 1990 |
| Johnson Trade Solutions Ltd | Wholesale & retail | 2024 |
| Johnston Campbell Holdings Limited | Financial services | 2010 |
| Johnston Carson Business Solutions Ltd | Administrative & support | 2021 |
| Johnston Kennedy Ltd | Professional & scientific | 2013 |
| Johnston Properties Ltd | Real estate | 2021 |
| Johnston Properties N.I. Ltd | Real estate | 2026 |
| Johnston Roofing Ltd | Construction | 2025 |
| Johnstondavey Commercial Finance Limited | Financial services | 2019 |
| Johnstongrieve BK Limited | Professional & scientific | 2024 |
| Johnstongrieve CA Limited | Financial services | 2019 |
| Johome Limited | Wholesale & retail | 2023 |
| Joiiiful Therapies Ltd | Other services | 2024 |
| Joinery Cottage Ltd | Construction | 2024 |
| Joinme Trading Limited | Wholesale & retail | 2025 |
| Jojoma Limited | Wholesale & retail | 2024 |
| Joker Tattoo Company Limited | Other services | 2017 |
| Joma Tunneling Ltd | Construction | 2026 |
| Jomada Engineering Ltd | Manufacturing | 2016 |
| JON Belshaw Ltd | Water & waste | 2016 |
| JON Electrical Ltd | Construction | 2013 |
| Jona Developments Limited | Real estate | 1999 |
| Jonathan Corr Ltd | Wholesale & retail | 2025 |
| Jonathan Dawson Ltd | Wholesale & retail | 2025 |
| Jonathan Dunn Ltd | Manufacturing | 2022 |
| Jonathan Finlay Private Wealth Limited | Financial services | 2020 |
| Jonathan Keys Ballyhackamore Limited | Wholesale & retail | 2018 |
| Jonathan Keys Limited | Wholesale & retail | 2007 |
| Jonathan Riddell Sound Ltd | Arts & recreation | 2022 |
| Joncon Property Enterprises Ltd | Households | 2024 |
| Jones Events and Catering Company Ltd | Hospitality | 2026 |
| Jones GAS Services Limited | Construction | 2019 |
| Jones Wisdom Trading Limited | Wholesale & retail | 2024 |
| Joni Cash Limited | Professional & scientific | 2013 |
| Jonny Greig Ltd | Professional & scientific | 2021 |
| Jonny Reid Limited | Other services | 2023 |
| Jonthree Trust Limited | Other services | 2000 |
| Jon’S Hammer Ltd | Manufacturing | 2024 |
| Joojinta LLP | | 2014 |
| Jopec Developments Limited | Real estate | 2007 |
| Jora Digital Solutions Limited | Information & communication | 2026 |
| Jora Properties Ltd | Real estate | 2019 |
| Jordan Consultancy Services Limited | Professional & scientific | 2020 |
| Jordan Estates Limited | Real estate | 2026 |
| Jordan Patmore Golf & Fitness Ltd | Arts & recreation | 2023 |
| Jordan Plastics Limited | Extraterritorial | 1973 |
| Jordanne Asha Ventures Limited | Wholesale & retail | 2019 |
| Jordans Home Bakery Ltd | Manufacturing | 2005 |
| Jordanstown Grange Limited | Households | 1987 |
| Jory Yulia Ltd | Wholesale & retail | 2025 |
| Jose's Deli Hillview Ltd | Hospitality | 2022 |
| Jose's Food Truck Ltd | Hospitality | 2026 |
| Jose's to Go Limited | Hospitality | 2025 |
| Joseph Blair (Belfast) Limited | Wholesale & retail | 2026 |
| Joseph Hughes Car Sales Limited | Wholesale & retail | 2015 |
| Joseph REA Jewellers Limited | Manufacturing | 2004 |
| Joseph REA Productions Ltd | Arts & recreation | 2012 |
| Joseph Scott Hairdressing Ltd | Other services | 2017 |
| Josh Taylor Coaching Limited | Health & social care | 2023 |
| Joshua Ella Ltd | Other services | 2018 |
| Jossers Limited | Administrative & support | 2020 |
| Jossevi Limited | Construction | 2007 |
| Josten Ltd | Financial services | 2024 |
| Joule Alliance LP | | 2017 |
| Journely Ltd | Information & communication | 2025 |
| Journeyfor Business Ltd. | Information & communication | 2014 |
| Joxer Holywood Limited | Hospitality | 2023 |
| Joy EAT Limited | Hospitality | 2025 |
| Joya Sleep UK Limited | Manufacturing | 2022 |
| Joyce Associates Limited | Professional & scientific | 2021 |
| Joyce Wells Limited | Other services | 2017 |
| Joyexa Ltd | Professional & scientific | 2026 |
| Joyful Fortune Ltd | Wholesale & retail | 2024 |
| Joylol Limited | Wholesale & retail | 2023 |
| Joymore Limited | Real estate | 1954 |
| Jozmm Zeooa Ltd | Wholesale & retail | 2024 |
| JP Accounting Limited | Professional & scientific | 2023 |