| Macren Ltd | Other services | 2006 |
| Macroney Limited | Construction | 2020 |
| MAD Mowers Ltd | Manufacturing | 2023 |
| Maddison MAE Organisation CIC | Health & social care | 2025 |
| Made in Dorset Limited | Hospitality | 2012 |
| Made Property Services Limited | Administrative & support | 2017 |
| Magical Toy Shop Ltd | Wholesale & retail | 2018 |
| Mahi Properties Ltd | Real estate | 2020 |
| Maiden Dorset Limited | Wholesale & retail | 2013 |
| Maiden House Management Company Limited | Real estate | 2016 |
| Maiden Newton Clearance Ltd | Administrative & support | 2022 |
| Maiden Newton Garage Limited | Wholesale & retail | 2021 |
| Maiden Newton Management Company Limited | Households | 1995 |
| Maiden View Court Management Company Limited | Households | 2013 |
| Mailability Limited | Transport & logistics | 2002 |
| Maintain My Home Limited | Construction | 2013 |
| Maintenance Managed Limited | Construction | 2024 |
| Maison's Property Investment Limited | Real estate | 2017 |
| Maitland Travel Limited | Administrative & support | 2018 |
| Major Boiler Services Ltd | Manufacturing | 2011 |
| Major Golf (U.K.) Limited | Wholesale & retail | 2000 |
| Major Golf Enterprises Ltd | Arts & recreation | 2014 |
| Make Space (Hub) Ltd | Professional & scientific | 2021 |
| Maki Japanese Restaurant Limited | Hospitality | 2010 |
| Malcolm Goodyear Carpentry & Building Services Limited | Construction | 2003 |
| Malthouse SIX Limited | Households | 2005 |
| Manida Venture Holdings Ltd | Wholesale & retail | 2017 |
| Manna Kitchen Ltd | Hospitality | 2013 |
| Manor Cottages Management Limited | Households | 1997 |
| Manor Court (Bishops Caundle) Property Management Company Ltd | Households | 2018 |
| Manor Farm Cottages Limited | Households | 2002 |
| Manor Farm Dairy Limited | Agriculture & fishing | 2007 |
| Manor Farm Galton Limited | Agriculture & fishing | 2003 |
| Manor Park Flooring Limited | Wholesale & retail | 2013 |
| Mansell House Management Company Limited | Households | 2004 |
| Manta Expeditions Limited | Other services | 2013 |
| Mantlet Consulting Limited | Public administration | 2017 |
| Manton Ltd | Wholesale & retail | 2021 |
| Manuka Capital Ltd | Financial services | 2023 |
| Maramba & Associates Limited | Professional & scientific | 2017 |
| Marbledoor Limited | Real estate | 2004 |
| Marc Saunders Consulting Ltd | Professional & scientific | 2017 |
| March and Meldrum Ltd | Administrative & support | 2024 |
| Marchant Decorating Ltd | Construction | 2022 |
| Marcia Headon Education Limited | Administrative & support | 2016 |
| Margherita Maggio Limited | Wholesale & retail | 2022 |
| Maria's Way Limited | Health & social care | 2017 |
| Marine Check Ltd | Professional & scientific | 2025 |
| Marine Inspection Services Limited | Manufacturing | 2006 |
| Marinex LNG Ltd | Transport & logistics | 2026 |
| Maritime House West Bay Limited | Administrative & support | 2005 |
| Maritime Towing Services Limited | Transport & logistics | 2016 |
| Mark Benfield Limited | Other services | 2011 |
| Mark Boyden Limited | Other services | 2022 |
| Mark Collett Plastering Contractor LLP | | 2013 |
| Mark Davis Mortgages Limited | Financial services | 2023 |
| Mark Hitchcock Ltd | Health & social care | 2026 |
| Mark Whitely (Dorset) Limited | Construction | 2015 |
| Mark Whitely Group Limited | Construction | 2000 |
| Mark Whitely Plant Hire Limited | Construction | 2005 |
| Mark Wilton-Patrick Ltd | Administrative & support | 2018 |
| Market Hall Management Company Limited | Households | 2023 |
| Marketing West SW Ltd | Professional & scientific | 2012 |
| Markham Management Company Limited | Real estate | 2018 |
| Marlborough Road Management Ltd. | Households | 1999 |
| Marlex Leisure Ltd | Wholesale & retail | 2025 |
| Marmotte Properties Limited | Real estate | 2011 |
| Marrith Limited | Financial services | 2023 |
| Marshmallow Avenue Limited | Manufacturing | 2024 |
| Martagon Holidays Ltd | Administrative & support | 1978 |
| Martin Andrews Planning Consultancy Limited | Professional & scientific | 2013 |
| Martin Baker Consulting Limited | Wholesale & retail | 2013 |
| Martin Donlin Limited | Administrative & support | 2002 |
| Martin Homes Dorset Limited | Construction | 2020 |
| Martin Smith Roofing Services Ltd | Construction | 2022 |
| Martyn's Law Compliance Limited | Information & communication | 2026 |
| Marvey Ltd | Manufacturing | 2025 |
| Marylebone Developments Limited | Real estate | 2014 |
| Mason Security Limited | Information & communication | 2004 |
| Maspero Associates Wealth Management Limited | Financial services | 2015 |
| Mastland Ltd | Professional & scientific | 2022 |
| Matanna Construction Limited | Construction | 2020 |
| Matilda Barrowcliff Limited | Professional & scientific | 2025 |
| Matthes Subsea Limited | Professional & scientific | 2011 |
| Matthew Lucas Funeral Directors Ltd | Other services | 2013 |
| Matthil Ltd | Hospitality | 2024 |
| Maurward Close Management Company Limited | Households | 2023 |
| MAX 25 Limited | Real estate | 2024 |
| MAX Gate Digital Ltd | Information & communication | 2010 |
| MAX Shutler Plumbing & Heating Limited | Construction | 2016 |
| Maximo Recio Limited | Professional & scientific | 2023 |
| MAY Bower Gardens Management Company Ltd | Households | 2023 |
| MAY Family Holdings Limited | Financial services | 2018 |
| Maycroft Bourton Management Company Ltd | Households | 2020 |
| Mayflower Leasing Limited | Wholesale & retail | 2013 |
| MBC Bird & Pest Solutions Limited | Agriculture & fishing | 2013 |
| MBS Dorchester Limited | Construction | 2015 |
| MC Motor Services Limited | Wholesale & retail | 2019 |
| MCB Civil Engineering Limited | Construction | 2008 |
| MCB International Ltd | Extraterritorial | 2025 |