| Lynn Gilbert Design Ltd | Professional & scientific | 2017 |
| M a Harding Properties Ltd | Real estate | 2024 |
| M J Hartnett Property Investments Limited | Construction | 2018 |
| M.J.H. Property Developments Limited | Construction | 1984 |
| Macellum Estate Management Company Limited | Households | 2003 |
| Mahah Property Ltd | Extraterritorial | 2022 |
| Mait Fuel Limited | Arts & recreation | 2025 |
| Maizi Holdings Ltd | Real estate | 2025 |
| Mallard Maintenance Limited | Households | 1997 |
| Manor Farm PV Limited | Energy | 2023 |
| Marama Gardens Management Limited | Households | 1992 |
| Marble Developments Ltd | Construction | 2020 |
| Marble Electrical Contractors Limited | Construction | 2014 |
| Marble M&E Group Ltd | Construction | 2017 |
| Marble Plumbing and Heating Limited | Construction | 2017 |
| Marchwood Management (Chichester) Limited | Households | 1983 |
| Mariners RTM Company Limited | Households | 2015 |
| Marineside (Residents' Association) Limited | Households | 1971 |
| Marlen Consulting Ltd | Information & communication | 2011 |
| Marlin Solutions Ltd | Information & communication | 2021 |
| Maxim Residential Ltd | Construction | 2013 |
| Mayfair Court Management Company (Chichester) Limited | Households | 1995 |
| Mayfield Place (Yapton) Management Company Limited | Households | 2006 |
| MBM (West Sussex) Limited | Professional & scientific | 2009 |
| MC Prado Logistics Ltd | Transport & logistics | 2021 |
| Meaux Fields Solar Limited | Energy | 2022 |
| Megan Eleanor Hair Ltd | Other services | 2026 |
| Melville LEE Gardens Ltd | Households | 2023 |
| Memorial Stone Centre Limited | Other services | 1999 |
| Mendip Wood Management Company Limited | Households | 1974 |
| MGT Property Ltd | Real estate | 2020 |
| Michael Harding Ltd | Professional & scientific | 2021 |
| Midnight Wave Ltd | Financial services | 2026 |
| Miles Cleall Sales Agency Ltd | Professional & scientific | 2012 |
| Millhouse (Broadbridge) Management Limited | Households | 1995 |
| Mind Your Wildlife Manors Ltd | Professional & scientific | 2016 |
| Mineralfields Ltd | Administrative & support | 2014 |
| Miracle Minds Ltd | Education | 2024 |
| Mirza & Nacey Research Limited | Information & communication | 2002 |
| Misslebrooks Storage Facility Limited | Energy | 2022 |
| Mitka Art Ltd | Arts & recreation | 2025 |
| Mitmakes Limited | Manufacturing | 2013 |
| MJH Property Investments LLP | | 2009 |
| MMG Knitwear Limited | Wholesale & retail | 2022 |
| Momentsofarundel Ltd | Hospitality | 2025 |
| Momentum Business Support Ltd | Administrative & support | 2013 |
| Monster Grab Hire Ltd | Water & waste | 2026 |
| Moozi Creative Limited | Administrative & support | 2006 |
| Mopani Trading Limited | Wholesale & retail | 2009 |
| Moss OFF Roof (West Sussex) Ltd | Administrative & support | 2025 |
| Mowbray House Management Company Limited | Households | 2017 |
| Moxey Ltd | Information & communication | 2014 |
| Murray Equipment Company Limited | Manufacturing | 1976 |
| N-Gin Recruitment Ltd | Administrative & support | 2022 |
| N-Gin Trade School Ltd | Education | 2026 |
| Natural Art Studio Ltd | Wholesale & retail | 2023 |
| Naturewild Forest School Ltd | Education | 2021 |
| Navigate-Us Limited | Information & communication | 2007 |
| New AU Pair Limited | Other services | 2005 |
| New Beginnings Health Ltd | Health & social care | 2019 |
| Newnham BA Services Ltd | Information & communication | 2013 |
| Newtons Mercedes Benz Specialists LLP | | 2018 |
| Nexus Junto Ltd | Information & communication | 2025 |
| NH Logistics Ltd | Professional & scientific | 2022 |
| Nomadic Enterprises Ltd | Construction | 2024 |
| Nordicon Limited | Professional & scientific | 1995 |
| Norfolk Estate Farms Limited | Agriculture & fishing | 1997 |
| Norfolk Trustees Limited | Professional & scientific | 1989 |
| Normans Coffee Ltd | Hospitality | 2025 |
| North Lane Generation Hub Limited | Energy | 2024 |
| North Marlborough Ltd | Real estate | 2013 |
| Nursery Mews (Chichester) Management Company Limited | Households | 2014 |
| Nuts About Bolts Ltd | Manufacturing | 2000 |
| NW Leasing Solutions Ltd | Administrative & support | 2023 |
| Oaks Management (Fishbourne) Limited | Households | 2015 |
| Oando Consulting Limited | Information & communication | 2012 |
| Occupational Testing Limited | Professional & scientific | 1988 |
| Octopod Kayak Hire Limited | Administrative & support | 2023 |
| Offham Assets Limited | Financial services | 1990 |
| OGW Property Solutions Ltd | Construction | 2020 |
| Ohme Electrical Serivices Ltd | Construction | 2025 |
| Okoa Ltd | Education | 2021 |
| Old School (Reading Street) Residents Management Company Ltd | Households | 2025 |
| Old School Place (Hove) Management Limited | Households | 2005 |
| Oldland Investments Limited | Construction | 2021 |
| Olive Stone Skin Clinic Ltd | Other services | 2025 |
| Olivers Court Limited | Households | 2003 |
| ON the Cobbles Ltd | Hospitality | 2026 |
| Ongar Investments Limited | Real estate | 1962 |
| Only Aesthetics Ltd | Health & social care | 2025 |
| Open Sussex Ltd | Information & communication | 2018 |
| Optimum.Aero Limited | Wholesale & retail | 2015 |
| Optimus Stables Ltd | Agriculture & fishing | 2023 |
| Optume UK Limited | Information & communication | 2026 |
| Orca Recruiter Systems Limited | Information & communication | 2026 |
| Organised Docs Ltd | Administrative & support | 2026 |
| Orkney Boats Limited | Manufacturing | 2013 |
| Orme Road (Worthing) Management Company Limited | Households | 2007 |
| Outside Inside Landscapes Ltd | Administrative & support | 2025 |
| Overacres Contracting Ltd | Agriculture & fishing | 2022 |