| North Down VIP Entertainment Ltd | Arts & recreation | 2017 |
| North Down Ymca | Health & social care | 2003 |
| North Hill Court RTM Company Limited | Households | 2009 |
| North Wales Computer Recycling Limited | Water & waste | 2023 |
| North Wales Contract Cleaning Limited | Administrative & support | 2017 |
| North Wales EYE Correction Centre Ltd | Health & social care | 2021 |
| North Wales Fencing Limited | Extraterritorial | 2023 |
| North Wales Glass Limited | Construction | 2024 |
| North Wales Heritage Group Ltd. | Administrative & support | 2017 |
| North Wales Highway Services Limited | Administrative & support | 2008 |
| North Wales Locations Limited | Information & communication | 2023 |
| North Wales Neuropsychology Services Ltd | Health & social care | 2015 |
| North Wales Radiology Limited | Health & social care | 2023 |
| North Wales Society for the Blind | Health & social care | 2011 |
| North Wales Solutions Ltd | Information & communication | 2025 |
| North Wales Spine Clinic Ltd | Health & social care | 2017 |
| North Wales Tree Consultancy Ltd | Professional & scientific | 2024 |
| North Wales Tree Surgery and Landscaping Limited | Administrative & support | 2026 |
| North Wales Wildlife Trust | Other services | 1963 |
| North West Wales Management Development Centre Limited | Hospitality | 2005 |
| Northern Card Gaming Ltd | Wholesale & retail | 2019 |
| Northern EEG Limited | Health & social care | 2008 |
| Northern Hospital Supplies Limited | Wholesale & retail | 1981 |
| Northern Ireland Forest School Association | Education | 2008 |
| Northern Ireland Heritage Gardens Trust- the | Arts & recreation | 2005 |
| Northern Light Innovation Ltd | Professional & scientific | 2011 |
| Northop Road Flint Limited | Construction | 2022 |
| Nova Facilities Services Ltd | Administrative & support | 2025 |
| Nova Robotics Ltd | Wholesale & retail | 2026 |
| Novus Enterprises Ltd | Professional & scientific | 2016 |
| Npgi Trading Limited | Hospitality | 2018 |
| NR Retail Limited | | 2005 |
| NS Property and Investments Ltd | Real estate | 2012 |
| NS2 Management Ltd | Real estate | 2013 |
| NSC Properties Ltd | Real estate | 2006 |
| Nu-Gentle Wellness Ltd | Other services | 2026 |
| NUC Inc Limited | Manufacturing | 2023 |
| Number 33 (Newcastle) Limited | Real estate | 2017 |
| Numberpress Limited | Real estate | 1995 |
| Nutrition Talent Limited | Health & social care | 2018 |
| NZE Supplies Ltd | Professional & scientific | 2026 |
| O Company UK Limited | Arts & recreation | 2005 |
| O D Works Ltd | Arts & recreation | 2020 |
| O'Boyle Accounting & Taxation Ltd | Professional & scientific | 2009 |
| O'Hara Design Services Ltd | Administrative & support | 2015 |
| O. Ramsden Limited | Health & social care | 2003 |
| Oberalp UK Limited | Wholesale & retail | 1996 |
| Ocean Discovery Limited | Arts & recreation | 1999 |
| Oceandrop Investments Limited | | 2006 |
| Octio Offsite (Wales) Ltd | Construction | 2025 |
| Octopistimuli Limited | Professional & scientific | 2021 |
| OF Mind Ltd | Manufacturing | 2016 |
| OF Right Mind Ltd | Professional & scientific | 2022 |
| Oghani Unlimited | Financial services | 2021 |
| Ogwen Accounts Limited | Professional & scientific | 2020 |
| Ogwen Joinery and Building CYF | Construction | 2019 |
| Ogwen Mussel Ltd | Agriculture & fishing | 2003 |
| Ogwen Physical Limited | Health & social care | 2023 |
| Ogwen Physical Rehabilitation Limited | Health & social care | 2023 |
| OHA Motorsport Limited | Wholesale & retail | 2016 |
| OHM Consulting Ltd | Professional & scientific | 2024 |
| Olah Products Ltd | Wholesale & retail | 2019 |
| Old Belfast Road Management Company Ltd | Households | 2004 |
| Old Mill Property Management Limited | Households | 2002 |
| Old Stone Resources Limited | Administrative & support | 2023 |
| Olel Limited | Real estate | 2024 |
| Olive Tree Eatery & Coffee House Ltd | Hospitality | 2024 |
| Ollie Axon Media Limited | Information & communication | 2017 |
| Olympic Fixings Ireland Ltd | | 1996 |
| OMA Foods Ltd | Wholesale & retail | 2026 |
| Ombler Williams Limited | Construction | 2002 |
| Ombler Williams Properties Ltd | Real estate | 2024 |
| Omniglot Limited | Information & communication | 2008 |
| ON Spot Crystal Ltd | Administrative & support | 2023 |
| One Equine Trust | Other services | 2020 |
| One Question Research Ltd | Professional & scientific | 2024 |
| Onega Centre Bath Limited | Construction | 2015 |
| Oneida Limited | | 1980 |
| Onshore Safety Consulting Limited | Professional & scientific | 2026 |
| ONZ Consulting Ltd | Information & communication | 2022 |
| Opal I.T. Services Ltd. | Information & communication | 2002 |
| Open Heavens Cafes CIC | Hospitality | 2025 |
| Open House Festival Limited | Arts & recreation | 2002 |
| Open House Trading Ltd | Arts & recreation | 2022 |
| Ophelia's Meadow Design Limited | Wholesale & retail | 2022 |
| Optimal Opportunity Limited | Information & communication | 2024 |
| Optimus IT Ltd | Information & communication | 2015 |
| Orchard Green Tax Limited | Professional & scientific | 2015 |
| Orets Limited | Construction | 2023 |
| Oriel 45 Ltd | Wholesale & retail | 2015 |
| Origin Renewables Ltd | Professional & scientific | 2014 |
| Original Telecoms Ltd | Information & communication | 2004 |
| Orpheus Creative Ltd | Professional & scientific | 2022 |
| Ortho@Holme Limited | Health & social care | 2021 |
| Oscan Limited | Administrative & support | 2025 |
| Oto-Ni-Pottery Ltd | Arts & recreation | 2024 |
| Ottersly Limited | Professional & scientific | 2020 |
| OUT & Active NI Community Interest Company | Administrative & support | 2024 |
| Owen & Davies Roofing and Solar Ltd | Construction | 2025 |
| Owen & Palmer Holdings Limited | Professional & scientific | 2004 |