| Moonbump Limited | Manufacturing | 2015 |
| Moonraker Project Management Ltd | Information & communication | 2018 |
| Moore Planning Limited | Professional & scientific | 2026 |
| Morari Earth Ltd | Information & communication | 2026 |
| Morgan Aviation Consultancy Ltd | Transport & logistics | 2008 |
| Morph Bricks Ltd | Manufacturing | 2021 |
| Morris Road Garage Limited | Extraterritorial | 2005 |
| Mortar Works Limited | Information & communication | 2019 |
| Mosaic Edge Limited | Professional & scientific | 2023 |
| Mount (Lewes) Residents' Association Limited(The) | Households | 1985 |
| Moveeasier Limited | Professional & scientific | 2006 |
| Movingsounds CIC | Education | 2006 |
| MP Motor Sport Limited | Arts & recreation | 2011 |
| Mplant Properties LLP | | 2019 |
| MR Cherry Picker Limited | Construction | 2018 |
| MR Cleaning Limited | Administrative & support | 2006 |
| MT Legacy Limited | Real estate | 2025 |
| MT Mobility Bath Co Ltd | Construction | 2025 |
| Much Adddo Accountants Limited | Professional & scientific | 2014 |
| Murph's Sips Ltd | Hospitality | 2026 |
| Musichall Limited | Arts & recreation | 2000 |
| MVP Property Limited | Real estate | 2019 |
| My Father's House Film Ltd | Information & communication | 2025 |
| My Glass Group Limited | Construction | 2023 |
| My Time to Dance Limited | Arts & recreation | 2025 |
| Mycroft Accounts Limited | Professional & scientific | 2024 |
| Myra Ventures Limited | Information & communication | 2013 |
| Nairne Consultancy Services Ltd | Professional & scientific | 2018 |
| Nakba Filmworks Ltd | Information & communication | 2012 |
| Namayasai LLP | | 2004 |
| Nanaco Limited | Wholesale & retail | 2022 |
| Nashi Club Limited | Other services | 2025 |
| NDA Home Improvements Ltd | Construction | 2024 |
| Neal's Yard Remedies (Brighton) Limited | Wholesale & retail | 2009 |
| Nekton Studio Limited | Professional & scientific | 2010 |
| NEN Trust | Education | 2010 |
| Nest Construction (Sussex) Ltd | Construction | 2024 |
| NET 1ON1 Wholesale Limited | Wholesale & retail | 2013 |
| NET Zero Pathfinders Limited | Professional & scientific | 2025 |
| Neural Intelligence Ltd | Information & communication | 2025 |
| Neuroscience for Wellbeing Limited | Professional & scientific | 2022 |
| Nevill Juvenile Bonfire Society CIC | Arts & recreation | 2024 |
| New Big Prinz Ltd | Hospitality | 2025 |
| New Dimension Homes Limited | Construction | 2021 |
| New Dimension Homes One Limited | Construction | 2024 |
| New Legal Services Limited | Professional & scientific | 2019 |
| New Notebook Ltd | Information & communication | 2026 |
| Newent GAS Services Limited | Construction | 2018 |
| Newhaven Green Centre CIC | Other services | 2022 |
| Newick Bonfire Society Limited | Arts & recreation | 1993 |
| Newick Wine Estate Limited | Manufacturing | 2021 |
| Newland Alliance Limited | Hospitality | 2023 |
| Newport Mining Limited | Financial services | 2012 |
| Nichols Crane Service Limited | Other services | 2020 |
| Nick Adams Architects Limited | Professional & scientific | 2018 |
| Nick Davies Limited | Administrative & support | 2006 |
| Nicola Furner Architects Limited | Professional & scientific | 2011 |
| Night Writer Ltd | Information & communication | 2024 |
| Nineteen Eighty One Ltd | Wholesale & retail | 2021 |
| Nitro Pest Control Ltd | Agriculture & fishing | 2025 |
| Njwe Limited | Real estate | 2020 |
| NM Touch Typing Ltd | Education | 2019 |
| NMD Marketing Ltd | Professional & scientific | 2021 |
| Nmpp Ltd | Real estate | 2024 |
| Nortec (Engineering) Limited | Professional & scientific | 1997 |
| North Corner Lewes Limited | Health & social care | 2016 |
| North Kensington Surveyor Limited | Professional & scientific | 2018 |
| North Street Garage Limited | Wholesale & retail | 2003 |
| Northease Manor School Limited | Education | 1972 |
| Norton-Smith Consulting Ltd | Professional & scientific | 2025 |
| NOSE2TAIL Butchers Limited | Wholesale & retail | 2026 |
| NOSE2TAIL Family Butchers LLP | | 2020 |
| Nova Light Capital Limited | Financial services | 2020 |
| Novalita Limited | Professional & scientific | 2021 |
| Novington Lane Ltd | Professional & scientific | 2021 |
| NOW Dance Ltd | Arts & recreation | 2025 |
| NOW! Charity Group Ltd | Water & waste | 1995 |
| NS Housing Limited | Real estate | 2017 |
| NTD Internet Solutions Limited | Information & communication | 2009 |
| Nudibranch Limited | Construction | 2023 |
| Nørd Inc Ltd | Wholesale & retail | 2005 |
| O&O MDC Limited | Administrative & support | 2001 |
| O'Sullivan Skoufoglou Architects Limited | Professional & scientific | 2017 |
| Oak and Stone Kitchens Ltd | Manufacturing | 2025 |
| Oak House Consulting Limited | Professional & scientific | 2011 |
| Oaklands Creative Limited | Wholesale & retail | 2024 |
| Oakleaf Property Group Limited | Construction | 2021 |
| Oakwayservices Limited | Administrative & support | 2024 |
| Oakwood Spa Limited | Transport & logistics | 2024 |
| Objective Focus Limited | Information & communication | 2014 |
| Obsolete Engineering Ltd | Wholesale & retail | 2025 |
| OH! Productions Limited | Arts & recreation | 2025 |
| OJT Wastewater Services Ltd | Professional & scientific | 2026 |
| Old Bear and Friends Limited | Administrative & support | 1991 |
| Old Forge (Home & Garden) Ltd | Wholesale & retail | 2011 |
| Old Grey Limited | Professional & scientific | 2025 |
| Old Tree Brewery C.I.C. | Manufacturing | 2018 |
| Old Tree Events Ltd | Hospitality | 2024 |
| Old Tree Soil Ltd | Administrative & support | 2020 |
| Oldenburg Training Center Ltd | Agriculture & fishing | 2023 |