| Major Plant Services Ltd | Construction | 2021 |
| Mane Street Management Ltd | Professional & scientific | 2023 |
| Manor Courtyard Management Company Limited | Households | 1998 |
| Manton Grange Stables Limited | Arts & recreation | 2014 |
| Manton Park Racing Limited | Agriculture & fishing | 1973 |
| Manton Park Residential Ltd | Real estate | 2020 |
| Manvers House Management Limited | Households | 2021 |
| Maplecircle Limited | Real estate | 1989 |
| Marathon Distribution Limited | Manufacturing | 1994 |
| Marby Properties Limited | Real estate | 2020 |
| March Racing Organisation Limited | Arts & recreation | 1993 |
| Marchstone Security Limited | Administrative & support | 2025 |
| Marlborough & Young Ltd | Construction | 2013 |
| Marlborough Antiques Ltd | Administrative & support | 2017 |
| Marlborough Arts Association | Arts & recreation | 1993 |
| Marlborough Aviation Consultants Ltd | Professional & scientific | 2025 |
| Marlborough Business Consulting Limited | Administrative & support | 2010 |
| Marlborough Chiropractic Clinic Ltd | Health & social care | 2022 |
| Marlborough College (Overseas) Limited | Education | 2007 |
| Marlborough College International Ltd | Education | 2019 |
| Marlborough Commercial Management Ltd | Professional & scientific | 2025 |
| Marlborough Curry Ltd | Hospitality | 2022 |
| Marlborough Downs Equestrian Services Limited | Arts & recreation | 1999 |
| Marlborough Festival CIC | Arts & recreation | 2021 |
| Marlborough Fitness & Performance Limited | Arts & recreation | 2013 |
| Marlborough Golf Club Limited | Arts & recreation | 2008 |
| Marlborough Group Fitness Ltd | Arts & recreation | 2019 |
| Marlborough Havens Limited | Education | 2014 |
| Marlborough HR Solutions Limited | Professional & scientific | 2011 |
| Marlborough Interiors (UK) Limited | Construction | 2010 |
| Marlborough Joinery Limited | Manufacturing | 2000 |
| Marlborough Landscapes Limited | Administrative & support | 2015 |
| Marlborough Lingerie Limited | Wholesale & retail | 2011 |
| Marlborough Literature Festival | Administrative & support | 2009 |
| Marlborough Nails Ltd | Other services | 2024 |
| Marlborough Peri Peri Ltd | Hospitality | 2019 |
| Marlborough Photo Laboratories Limited | Professional & scientific | 1992 |
| Marlborough Plumbing Co. Ltd | Energy | 2013 |
| Marlborough Property Services Limited | Construction | 2020 |
| Marlborough River Development Ltd. | Construction | 2016 |
| Marlborough Rugby Football Club Limited | Arts & recreation | 2015 |
| Marlborough Takeaway Ltd | Hospitality | 2025 |
| Marlborough Vehicle Storage Ltd | Transport & logistics | 2026 |
| Marlborough.News Ltd | Information & communication | 2016 |
| Marmaduke Travel Ltd | Administrative & support | 2026 |
| Marquee Vision Limited | Administrative & support | 2007 |
| Marsh House Owners Ltd | Real estate | 2015 |
| Marshwood Professional Services Limited | Information & communication | 2001 |
| Martaven LP | | 2021 |
| Martel Lending Limited | Financial services | 2019 |
| Martel Northern Limited | Financial services | 1989 |
| Martyn Meade Racing LLP | | 2025 |
| Mason Adams Associates Limited | Professional & scientific | 2012 |
| Masons Mews Management Company Limited | Extraterritorial | 2013 |
| Master Inns Ltd | Hospitality | 2024 |
| Mather Rice Homes Ltd | Households | 2025 |
| Matrix Foot and Ankle Ltd | Health & social care | 2024 |
| Mattaeus Sports Management Ltd | Arts & recreation | 2012 |
| Matthew Peck Construction EOT Ltd | Financial services | 2025 |
| Matthew Peck Construction Ltd | Professional & scientific | 2016 |
| MAX Lynn Carpentry Limited | Construction | 2017 |
| Mayne Plumbing and Heating Services Ltd | Construction | 2023 |
| MB (Swindon) Limited | Construction | 2024 |
| MB2B Consultants Ltd | Professional & scientific | 2019 |
| MBI (Wilts) Ltd | Real estate | 2025 |
| Mcmarmilloyd Limited | Wholesale & retail | 2002 |
| Mcmillan Tait Limited | Arts & recreation | 1984 |
| MCS Umbrella Scheme Ltd | Construction | 2024 |
| MDH Solutions Limited | Professional & scientific | 2024 |
| Mdumbi Point Limited | Professional & scientific | 2024 |
| Meade Family Settlement Limited | Financial services | 2020 |
| Medaptive Ltd | Other services | 2017 |
| Media Pictures Limited | Information & communication | 2001 |
| Mehrangiz Limited | Real estate | 2019 |
| Meisner Dental Practice Business Services Ltd | Financial services | 2015 |
| Melin DDU Ltd | Information & communication | 2021 |
| Membury Development Limited | Construction | 2016 |
| Membury Estates Ltd | Agriculture & fishing | 2023 |
| Merchant's House Trading (Marlborough) Limited | Wholesale & retail | 1991 |
| Mere Consultants Limited | Professional & scientific | 2019 |
| Merlin's Pool Hall Ltd | Arts & recreation | 2021 |
| Merrow Associates Limited | Manufacturing | 2019 |
| Mezmo Events Ltd | Professional & scientific | 2019 |
| Michael Golden Consultancy Services Ltd | Information & communication | 2014 |
| Midway Stores Ltd | Wholesale & retail | 2018 |
| Mijato Limited | Manufacturing | 2022 |
| Mike Jessop Carpentry Limited | Construction | 2024 |
| Mil-Tech UK Limited | Professional & scientific | 2002 |
| Miles of Walks Ltd | Other services | 2026 |
| Milk Hill Limited | Professional & scientific | 2023 |
| Millfield James Limited | Health & social care | 2013 |
| Mills Corporate Advisory Limited | Professional & scientific | 2023 |
| Milton Architects Limited | Professional & scientific | 2005 |
| Milton Interiors Ltd | Professional & scientific | 2009 |
| Min's Kitchen Ltd | Hospitality | 2020 |
| Mind SET for Work Ltd | Public administration | 2025 |
| Mindassist Limited | Information & communication | 2023 |
| Minguet Limited | Manufacturing | 2016 |
| Mirabel Cosmetic Injections Limited | Administrative & support | 2001 |
| Mission Capital Ltd | Professional & scientific | 2013 |