| NT Engineering Consultant Ltd | Professional & scientific | 2025 |
| NT Engineering Ltd | Professional & scientific | 2015 |
| NT Leisure Ltd | Hospitality | 2025 |
| NTP Consett Ltd | Hospitality | 2026 |
| NTS Blade Tech Ltd | Construction | 2026 |
| Nucleus (GB) Limited | Hospitality | 2002 |
| Nuel Media Hub Limited | Information & communication | 2026 |
| Number 1 ST. Bedes Park Sunderland Limited | Real estate | 1994 |
| Number Cruncher Holding Limited | Professional & scientific | 2024 |
| Nurah’S Kitchen Ltd | Hospitality | 2026 |
| Nurture Healthcare Solutions Ltd | Public administration | 2023 |
| Nurture North C.I.C. | Health & social care | 2026 |
| Nurture Workspace Ltd | Wholesale & retail | 2021 |
| Nutrimax PES Limited | Wholesale & retail | 2024 |
| Nutrition Kingz NE Ltd | Manufacturing | 2024 |
| NV Collective Ltd | Hospitality | 2025 |
| NV Power Services Ltd | Construction | 2026 |
| NXT Chapter Ltd | Professional & scientific | 2022 |
| Nxt:Gen Holdings Limited | Real estate | 2023 |
| Nxt:Gen Investments Ltd | Financial services | 2022 |
| Nxtgen Fibre Ltd | Information & communication | 2025 |
| Nysera Ltd | Wholesale & retail | 2025 |
| O&G Events Ltd | Arts & recreation | 2022 |
| O'Brien Container Storage Limited | Transport & logistics | 2021 |
| O'Brien Specialist Crane Services Limited | Construction | 2019 |
| O'Brien Storage Limited | Transport & logistics | 2020 |
| O'Connors Garage Limited | Wholesale & retail | 2024 |
| O,S,I Rigging & Access Ltd | Construction | 2024 |
| Oakenshield Limited | Construction | 2022 |
| Oakgrove Ltd | Other services | 2019 |
| OAM (North East) Limited | Other services | 2024 |
| Oasis Glow Official Ltd | Wholesale & retail | 2026 |
| Oasis Tipis Limited | Manufacturing | 2017 |
| Obawinsome Global Ltd | Professional & scientific | 2026 |
| Obifem Limited | Transport & logistics | 2024 |
| Objjames Clothing Accessories Ltd | Wholesale & retail | 2021 |
| Occasio Limited | Administrative & support | 2026 |
| Occh Management Ltd | Professional & scientific | 2023 |
| Occlusion Denture Laboratory Limited | Health & social care | 2012 |
| Occupational Health North East Ltd | Health & social care | 2007 |
| Ocean Micro PUB Limited | Hospitality | 2020 |
| Oceander Abodes Ltd | Health & social care | 2021 |
| Oceander LLP | | 2021 |
| Oceanic North Limited | Hospitality | 2017 |
| Octavioraz Limited | Households | 2025 |
| Octoba Limited | Information & communication | 2014 |
| Octomist Ltd | Information & communication | 2019 |
| Octopus One Consulting Ltd | Professional & scientific | 2024 |
| Oculus-Hr Limited | Administrative & support | 2013 |
| Odin Shipping Limited | Transport & logistics | 1977 |
| Odysseus Finance Limited | Professional & scientific | 2021 |
| Offerton Granaries Management Limited | Real estate | 2018 |
| Ofina Hair and Beauty Supplies Ltd | Wholesale & retail | 2024 |
| Ofmaerospace Ltd | Manufacturing | 2023 |
| OG Estate Services Ltd | Real estate | 2022 |
| Ogden Search Ltd | Administrative & support | 2026 |
| Ogines Wellbeing Limited | Health & social care | 2021 |
| Oikia Christian Centre UK Ltd | Other services | 2021 |
| OIL and GAS Management Services Limited | Professional & scientific | 2014 |
| Oiltec UK Limited | Professional & scientific | 2007 |
| Ojas Go Local Limited | Wholesale & retail | 2023 |
| OJC Properties Ltd | Real estate | 2024 |
| Okoroji Technologies Ltd | Professional & scientific | 2025 |
| Old PUB Kitchen Ltd | Hospitality | 2025 |
| Old Skool Builds and Roofing Limited | Construction | 2025 |
| Old ST Marks Care Ltd | Health & social care | 2023 |
| Olinor Properties Ltd | Real estate | 2024 |
| Olive Grove Learning Ltd | Education | 2021 |
| Olivias Coffee House Ltd | Hospitality | 2015 |
| Ollie Rose PMC Ltd | Other services | 2019 |
| Ollyfaith Consulting Ltd | Professional & scientific | 2019 |
| Ollyfaith Ventures Ltd | Wholesale & retail | 2022 |
| OLS Investments Ltd | Financial services | 2023 |
| Omnicasa Wholesale Ltd | Wholesale & retail | 2025 |
| Omninet Fibre Solutions Ltd | Professional & scientific | 2023 |
| Omninet Utility Solutions Limited | Construction | 2025 |
| Omoba General Services Limited | Transport & logistics | 2024 |
| ON the Line Construction Ltd | Construction | 2022 |
| ON to the Next Ltd | Professional & scientific | 2025 |
| One Life With Sensational Sounds Global PR Management Ltd | Arts & recreation | 2023 |
| One March Digital Ltd | Professional & scientific | 2024 |
| One Point Four West Ltd | Professional & scientific | 2026 |
| One Roker Terrace Limited | Hospitality | 2024 |
| One Source Utility Limited | Professional & scientific | 2025 |
| One Strategic Limited | Professional & scientific | 2022 |
| One Thing Matters Ltd | Transport & logistics | 2024 |
| Oneaura Limited | Wholesale & retail | 2025 |
| Onepotplant Company Ltd | Agriculture & fishing | 2021 |
| Only Tanzz Ltd | Other services | 2025 |
| Onyx Gate Residential Limited | Households | 2025 |
| Onyx Project Services Ltd | Construction | 2002 |
| Onyx Scientific Limited | Manufacturing | 2000 |
| Open Air Events 23 Ltd | Wholesale & retail | 2023 |
| Open Space Holdings Ltd | Financial services | 2019 |
| Opera Sunderland | Arts & recreation | 2014 |
| OPM Hairs Limited | Wholesale & retail | 2025 |
| Opodo World Limited | Professional & scientific | 2026 |
| Optihealth Healthcare Services Ltd | Health & social care | 2023 |
| Optihealth Property Limited | Real estate | 2026 |
| Optima Consulting Engineers Limited | Professional & scientific | 2020 |