| Nusite Limited | Information & communication | 2020 |
| Nutrition Boost Ltd | Wholesale & retail | 2025 |
| Nuwa & Nazgull Ltd | Other services | 2022 |
| NW FTM Consulting Ltd | Professional & scientific | 2015 |
| NWF Decorating Contractors Ltd | Construction | 2026 |
| Nwocc Ltd | Other services | 2025 |
| NX Properties Ltd | Hospitality | 2026 |
| NY Inspection Limited | Professional & scientific | 2007 |
| Nyrkio Ltd | Information & communication | 2023 |
| O & C Build Ltd | Construction | 2023 |
| O. and M. Electrical Services Limited | Construction | 1987 |
| Oak Kitchens Limited | Construction | 2023 |
| Oakbridge Beverages Ltd | Wholesale & retail | 2026 |
| Oakmere Kitchens Ltd | Other services | 2025 |
| Oakscroft Properties Ltd | Real estate | 2020 |
| Oasis Healthcare Consulting Ltd | Health & social care | 2023 |
| Oats Royd Mill Management Company Limited | Households | 2002 |
| OAY Accountancy Limited | Professional & scientific | 2024 |
| Obaa Holdings Ltd | Financial services | 2019 |
| Obesity UK Ltd | Health & social care | 2012 |
| Obhielo & Obhielo Legacy Holdings Limited | Real estate | 2026 |
| OBS Cleaning Services Ltd | Administrative & support | 2024 |
| Obsidian Trade Ltd | Wholesale & retail | 2025 |
| Obsigno Design Limited | Information & communication | 2004 |
| Obviously Agile Ltd | Information & communication | 2017 |
| Ockham Hydrogen Limited | Information & communication | 2023 |
| Oddyssey Glass Ltd | Construction | 2022 |
| Ofcc (Halifax) Limited | Manufacturing | 2017 |
| OFF Piste Pictures Limited | Information & communication | 2019 |
| Office in a Box Ltd | Professional & scientific | 2008 |
| Offshoot Operations Limited | Information & communication | 2013 |
| OG Dent Removal Ltd | Manufacturing | 2023 |
| Ogden Investments Limited | Real estate | 1996 |
| Ogden Otters Swim Academy Limited | Education | 2025 |
| Ogdenuk Ltd | Wholesale & retail | 2021 |
| OGK Consulting Ltd | Other services | 2017 |
| Ohalloran & Family Ltd | Construction | 2025 |
| Ohasys Software Limited | Information & communication | 2025 |
| OHY Services Ltd | Health & social care | 2024 |
| Oicengineering Limited | Construction | 2023 |
| OIL & GAS Subsea Production Systems Ltd | Professional & scientific | 2006 |
| OIL IS Well Ltd | Wholesale & retail | 2018 |
| OIR Properties Ltd | Real estate | 2024 |
| OK Let's Play Limited | Education | 2026 |
| Olaa Properties Limited | Real estate | 2022 |
| Old Brodleians Rugby Union Football Club Limited | Arts & recreation | 2017 |
| Old Brodleians Trading Company Limited | Arts & recreation | 2017 |
| Old Lane Autos Limited | Wholesale & retail | 2025 |
| Old Masonic Hall Hebden Bridge Limited | Professional & scientific | 2024 |
| Oldfield Bespoke Joinery Ltd | Construction | 2022 |
| Oldroyd Properties Limited | Professional & scientific | 2013 |
| Olicana 17 Consulting Services Ltd | Professional & scientific | 2023 |
| Olimi Ltd | Wholesale & retail | 2023 |
| Olive ASH Ltd | Wholesale & retail | 2025 |
| Oliver James Logistics Ltd | Transport & logistics | 2025 |
| Oliver LEE Salon Limited | Other services | 2014 |
| Oliver Rose Properties Ltd | Real estate | 2022 |
| Olivita Express Ltd | Hospitality | 2025 |
| Olivrose & Co Ltd | Other services | 2016 |
| Omega Proteins Limited | Manufacturing | 1999 |
| Omega Scaffolding of Halifax Limited | Construction | 2021 |
| OMY Beauty Ltd | Other services | 2020 |
| OMY Nails Limited | Other services | 2019 |
| ON a Roll (Blackburn) Limited | Wholesale & retail | 2018 |
| ON the Move West Yorkshire Limited | Transport & logistics | 2016 |
| One Call Construction & Maintenance Ltd | Construction | 2025 |
| One Love Properties Ltd | Real estate | 2021 |
| One OFF Circle Ltd | Hospitality | 2019 |
| One Small Key Limited | Professional & scientific | 2017 |
| Oneclick Healthcare Limited | Health & social care | 2017 |
| Oneclickshopping Ltd | Wholesale & retail | 2020 |
| Oneness Properties Ltd | Real estate | 2025 |
| Oneness Ventures Ltd | Professional & scientific | 2024 |
| Online Cards Ltd | Wholesale & retail | 2024 |
| Online Gadgetz UK Ltd | Wholesale & retail | 2022 |
| Only Good Things Ltd | Information & communication | 2016 |
| Only Projects Ltd | Arts & recreation | 2013 |
| Ontrack Groundworks Limited | Construction | 2009 |
| Onyx Camber Limited | Professional & scientific | 2019 |
| Onyx Repair Innovations Limited | Wholesale & retail | 2024 |
| Onyxridge Ltd | Health & social care | 2025 |
| Open Gallery CIC | Wholesale & retail | 2024 |
| Open Outfit Limited | Wholesale & retail | 2022 |
| Openpeak Digital Ltd | Wholesale & retail | 2025 |
| Operational Design and Construction Ltd | Professional & scientific | 2023 |
| OPL Leisure Group Ltd | Hospitality | 2003 |
| OPO Halifax 2020 Ltd | Hospitality | 2020 |
| Optica Management and Consultancy Ltd | Professional & scientific | 2022 |
| Opticare EYE Care Specialists Ltd | Wholesale & retail | 2013 |
| Optima Housing Consultants Limited | Professional & scientific | 2002 |
| Optima Locums Limited | Health & social care | 2012 |
| Optima Online Solutions Limited | Other services | 2021 |
| Optimal Car Detailing Ltd | Administrative & support | 2023 |
| Optimal Homecare Services Ltd | Health & social care | 2016 |
| Optimal Property Group Ltd | Real estate | 2026 |
| Optimal Windows and Doors Ltd | Construction | 2022 |
| Optimed Healthcare Solutions Ltd | Health & social care | 2024 |
| Optimise Consulting Group Ltd | Professional & scientific | 2023 |
| Optimosolutions Limited | Wholesale & retail | 2017 |
| Optimus Building Solutions Limited | Construction | 2009 |