| Mark Farwell Plant Hire Limited | Construction | 1994 |
| Mark Hardy Stonemasons Limited | Construction | 2014 |
| Mark Reid Windows Limited | Construction | 2001 |
| Mark Richards Motor Repairs Limited | Wholesale & retail | 2023 |
| Mark Sherratt Limited | Construction | 2013 |
| Mark Stebbing Carpets & Flooring Limited | Wholesale & retail | 2012 |
| Mark's Car Services Ltd | Wholesale & retail | 2023 |
| Marpro Services Limited | Transport & logistics | 2008 |
| Marquis Precision Engineering Company Limited | Manufacturing | 1977 |
| Martello Mews RTM Company Limited | Administrative & support | 2010 |
| Martin Green Interiors Limited | Wholesale & retail | 2019 |
| Martleaves Cottages Limited | Construction | 2026 |
| Martleaves Farm and Campsite Limited | Agriculture & fishing | 2023 |
| Martleaves Farm Campsite LLP | | 2022 |
| MAS Offshore Consultants Ltd | Energy | 2025 |
| Masala Restaurant Ltd | Hospitality | 2024 |
| Mason Management Ltd | Professional & scientific | 2024 |
| Massandra Court Limited | Households | 2021 |
| Master Merchant Limited | Wholesale & retail | 2023 |
| Masterplan Offshore Limited | Construction | 2013 |
| Masters of Fasteners Ltd | Wholesale & retail | 2019 |
| Matrix Scaffolding Dorset Limited | Construction | 2018 |
| Maverick (Weymouth) Limited | Agriculture & fishing | 1996 |
| MAW Group Ltd | Wholesale & retail | 2020 |
| MAX Ravenhall Cladding Limited | Construction | 2022 |
| Maxlyn Development Co. Limited | Real estate | 1974 |
| Maxpro-Solutions 2025 Ltd | Financial services | 2025 |
| Maxwell Properties (SW) Limited | Real estate | 2024 |
| Mayan Roofing Systems Ltd | Manufacturing | 2020 |
| Mayne Estates Limited | Real estate | 2021 |
| Mayston Equestrian Limited | Wholesale & retail | 2022 |
| MB Financial Solutions Limited | Professional & scientific | 2022 |
| MBR Direct Sales Ltd | Wholesale & retail | 2022 |
| MC Poole Ltd | Real estate | 2016 |
| Mcbride Technologies Limited | Information & communication | 2014 |
| Mccuk Limited | Construction | 2025 |
| MCF Refurbishments Ltd | Construction | 2022 |
| Mcgiso Limited | Professional & scientific | 2012 |
| MCH Baby Gifts Limited | Wholesale & retail | 2017 |
| Mcis Engineers Ltd | Professional & scientific | 2025 |
| Mdina Italia Ltd. | Wholesale & retail | 2020 |
| Medicare Recruitment Specialists Limited | Administrative & support | 2023 |
| Medipost (U.K.) Limited | Wholesale & retail | 1989 |
| Medisave (UK) Limited | Wholesale & retail | 2000 |
| Megginson Estates Limited | Real estate | 2019 |
| Melcombe Avenue Management Limited | Households | 2005 |
| Melcombe Avenue Residents Company Limited | Households | 1980 |
| Melcombe Court Management Company Limited | Households | 1998 |
| Melita Armitage Limited | Professional & scientific | 2009 |
| Mellstock Poultry Limited | Real estate | 1977 |
| Mellstock Technology Limited | Professional & scientific | 1991 |
| Mellstock Water Limited | Administrative & support | 1996 |
| Memo Pizzeria Limited | Hospitality | 2024 |
| Mentors (English) Limited | Education | 2006 |
| MEP Investments Limited | Real estate | 2015 |
| MER Engineering Limited | Professional & scientific | 2007 |
| Merchpanda Ltd | Manufacturing | 2024 |
| Mercury Retrograde Limited | Information & communication | 2025 |
| Merks Development Consultancy Ltd | Administrative & support | 2005 |
| Merlyn One Ltd | Wholesale & retail | 2018 |
| Merry Moos Farm Project CIC | Other services | 2021 |
| Meyndrina Ltd | Hospitality | 2026 |
| MF Business International Ltd | Wholesale & retail | 2024 |
| Mgdss Ltd | Professional & scientific | 2019 |
| Mgig Consultants Limited | Administrative & support | 2008 |
| MI Financial Consultants | | 2005 |
| Midland Craft Builders Ltd | Construction | 2015 |
| Midnight Media Digital Ltd | Professional & scientific | 2023 |
| Millar Plumbing & Heating Limited | Construction | 2012 |
| Milnes & Naerger Builders Limited | Construction | 2000 |
| Milwood Collection Ltd | Financial services | 2025 |
| Mind Therapy Limited | Administrative & support | 1999 |
| Mineral Engineering Limited | Professional & scientific | 2019 |
| Minster Furniture Company Limited | Manufacturing | 1996 |
| Mirari Lingerie Limited | Wholesale & retail | 2018 |
| Miss Tow-It-All Ltd | Transport & logistics | 2026 |
| Mission Fitness Limited | Health & social care | 2012 |
| Mister Klean Ltd | Other services | 2011 |
| MJ Scott Services Ltd | Construction | 2013 |
| MJ2231 Limited | Wholesale & retail | 2018 |
| MJC Aviation Ltd | Manufacturing | 2023 |
| MJF Consultancy Services Ltd | Professional & scientific | 2009 |
| MJP Consultancy Limited | Administrative & support | 2013 |
| MJS Design Solutions Ltd | Professional & scientific | 2009 |
| MJT Electrical Engineer Limited | Professional & scientific | 2014 |
| MK Marine Valves Ltd | Professional & scientific | 2018 |
| MLE Homes Limited | Real estate | 2025 |
| MLG Magazines Limited | Information & communication | 2012 |
| Moate & SON Property Maintenance Limited | Construction | 2014 |
| Moatt Sails Limited | Manufacturing | 2008 |
| Moderamen Ltd | Professional & scientific | 2026 |
| Modern Magazines Ltd | Information & communication | 2020 |
| Mona's Thai Limited | Hospitality | 2022 |
| Money Matters Financial Solutions Ltd | Financial services | 2009 |
| Monica Wolff Ltd | Professional & scientific | 2021 |
| Montserrat Management Co Limited | Households | 2023 |
| Mooqu Ltd | Wholesale & retail | 2026 |
| Moordown Ltd | Real estate | 2023 |
| Mooreatz Ltd | Hospitality | 2002 |
| Moreton Equestrian Limited | Administrative & support | 2005 |