| Nscript Limited | Information & communication | 2018 |
| NTM Transport Limited | Transport & logistics | 2024 |
| Nuabiome UK Limited | Health & social care | 2023 |
| Nufreight Ltd | Transport & logistics | 2023 |
| Numa Restaurant Limited | Hospitality | 2025 |
| Nvni Limited | Other services | 2016 |
| Nxtweb Ltd | Information & communication | 2025 |
| NY Diagnostic Ltd | Health & social care | 2025 |
| O Cantinho Portugues Ltd | Wholesale & retail | 2017 |
| O'Kane (Blue Rose Newco 1) Limited | Manufacturing | 2009 |
| O'Kane Poultry Limited | Manufacturing | 1964 |
| O.C.M Solutions Ltd | Wholesale & retail | 2021 |
| Oak House Surveyors Limited | Professional & scientific | 2005 |
| Oakdene Enterprises Limited | Financial services | 2012 |
| Oakfield Park Management Limited | Households | 2016 |
| Oakfield Park Manco Limited | Households | 2022 |
| Oakhill Haulage Limited | Transport & logistics | 2025 |
| Oaklands Management Company (Northern Ireland) Limited | Households | 2002 |
| Oaklands Specialist Contracts Limited | Construction | 2022 |
| Oakleaf Forestry Ltd | Manufacturing | 2016 |
| Oakwood Hall (Portadown) Management Limited | Households | 2019 |
| Oasis Group NI Limited | Administrative & support | 2003 |
| Oasis Youth Centre Limited | Arts & recreation | 1997 |
| Obitas Limited | Administrative & support | 2024 |
| OCL Richhill Management COY Limited | Households | 2019 |
| Octopus Centre for Heating Technology Limited | Professional & scientific | 2023 |
| Octopus Energy Production Limited | Manufacturing | 2014 |
| ODP247 Ltd | Health & social care | 2019 |
| Official Teamwear Ltd | Wholesale & retail | 2026 |
| OK Afie Ltd | Hospitality | 2025 |
| Old Church Management Limited | Households | 2016 |
| Old Coach Hill Management Limited | Households | 2012 |
| Old Coach Lane Management Company Limited | Households | 2012 |
| Old Gilford Road (Tandragee) Management Limited | Households | 2026 |
| Old Mill Court Management Tandragee NO.2 Limited | Households | 2021 |
| Old Mill Haulage Ltd | Transport & logistics | 2024 |
| Ollie’S Patisserie Ltd | Manufacturing | 2026 |
| Omega Health Care Solutions N.I Ltd | Health & social care | 2025 |
| Omerbane Limited | Financial services | 2019 |
| One-Ap Investments Limited | Financial services | 2022 |
| One-Ap Limited | Real estate | 2018 |
| Only PPC Limited | Professional & scientific | 2026 |
| Oocsmyth Limited | Real estate | 2025 |
| Oona Valley Community Association | Administrative & support | 1996 |
| Open Arms Church Limited | Other services | 2020 |
| Open Medscience Limited | Information & communication | 2025 |
| Optimal Innovations Ltd | Information & communication | 2025 |
| Orchard Cars Limited | Wholesale & retail | 1989 |
| Orchard Chippy Ltd | Hospitality | 2025 |
| Orchard County Investments Ltd | Professional & scientific | 1998 |
| Orchard County Property Solutions Ltd | Real estate | 2024 |
| Orchard Energy Solutions Limited | Construction | 2022 |
| Orchard Family Limited | Real estate | 2025 |
| Orchard Farm Foods Limited | Other services | 1999 |
| Orchard Lettings (Portadown) Limited | Real estate | 2019 |
| Orchard Linens Ltd | Wholesale & retail | 2019 |
| Orchard Rose Limited | Manufacturing | 2021 |
| Orchard Security Ltd | Administrative & support | 2022 |
| Orchard Wine Lodge Ltd | Wholesale & retail | 2010 |
| Orchardhill Enterprises Limited | Administrative & support | 1990 |
| Oriental Chef Lurgan Ltd | Hospitality | 2024 |
| Origin 71 Health & Fitness Ltd | Arts & recreation | 2021 |
| Orlagh Maye Salon Ltd | Other services | 2019 |
| Orodite Consulting Limited | Professional & scientific | 2015 |
| Orwell Investments NI Limited | Real estate | 2023 |
| OS Aesthetics Ltd | Other services | 2021 |
| Oscarhorizon Limited | Wholesale & retail | 2023 |
| Osel Properties NI Limited | Real estate | 2024 |
| OTE Contracts Ltd | Professional & scientific | 2023 |
| Ourweecountry Limited | Wholesale & retail | 2025 |
| Outlet Q Ltd | Wholesale & retail | 2026 |
| Ozanam Daycare Limited | Health & social care | 1998 |
| P and P Gilliland Holdings Ltd | Financial services | 2024 |
| P and P Gilliland Properties Ltd | Real estate | 2024 |
| P F Mcgovern Limited | Construction | 2015 |
| P H Agencies Ltd. | Wholesale & retail | 2010 |
| P MCC Medical Ltd | Health & social care | 2012 |
| P Mccann & Sons Limited | Extraterritorial | 2024 |
| P Nugent Builders Ltd | Construction | 2013 |
| P Travers Cladding Limited | Construction | 2018 |
| P V Thompson Ltd | Construction | 2020 |
| P&C Accountancy Ltd | Professional & scientific | 2025 |
| P&N Property Group Ltd | Real estate | 2023 |
| PAC Joinery Ireland Ltd | Construction | 2023 |
| Pactimo Ltd | Arts & recreation | 2016 |
| PADEL54DEGREESNORTH Ltd | Arts & recreation | 2023 |
| Paint Pots & Rollers Ltd | Construction | 2023 |
| PAL Surveying Ltd | Construction | 2018 |
| Pan!C LS Ltd | Transport & logistics | 2023 |
| Panda City Ltd | Hospitality | 2019 |
| Park Lane Development Management Company Limited | Households | 2002 |
| Parker G Interiors Limited | Construction | 2015 |
| Parkview Court (Lurgan) Management Company Limited | Households | 2001 |
| Partek Trading Limited | Wholesale & retail | 2017 |
| Partel Group Ltd | Financial services | 2022 |
| Partridge Business Solutions Ltd | Professional & scientific | 2021 |
| Partridge Construction Ltd | Construction | 2015 |
| Passive Homes Ltd | Professional & scientific | 2009 |
| PAT Vernon & Co Limited | Professional & scientific | 2018 |
| Pathway Consulting Limited | Administrative & support | 2025 |