| Management 24 Ltd | Hospitality | 2014 |
| Mandalay Villas Management Company Limited | Households | 2004 |
| Mandarin Garden Restaurant Ltd | Hospitality | 2011 |
| Mango Digital Marketing Ltd | Professional & scientific | 2016 |
| Mangoz Ltd | Real estate | 2023 |
| Maniglia-Scala Ltd | Administrative & support | 2017 |
| Mansion House Truro Ltd | Households | 2025 |
| MAP Network Group Ltd | Professional & scientific | 2012 |
| Maplesbark Ltd | Hospitality | 2022 |
| Marc Whitford Ltd | Construction | 2022 |
| Marcus Mccoan Ltd | Information & communication | 2019 |
| Marderholdings Ltd | Real estate | 2025 |
| Marine Court (ST. Mawes) Management Company Limited | Households | 1998 |
| Marine Fabrication and Engineering Ltd | Administrative & support | 2011 |
| Marine LAB Ltd | Manufacturing | 2021 |
| Marine Protective Coatings Ltd | Manufacturing | 2015 |
| Marine Sports Limited | Energy | 1985 |
| Marine Techniques Limited | Other services | 2008 |
| Mark Andrew Limited | Agriculture & fishing | 2010 |
| Mark Bolitho Construction Ltd | Construction | 2012 |
| Mark Datson Architectural Consultant Limited | Professional & scientific | 2007 |
| Mark Dawes Consultancy Limited | Professional & scientific | 1999 |
| Mark Watkins Haulage Ltd | Transport & logistics | 2015 |
| Market Taverns Limited | Hospitality | 1982 |
| Marketing in a Box Ltd | Professional & scientific | 2011 |
| Marsden Industries Ltd | Extraterritorial | 2025 |
| Marston & Heard Building & Civil Engineering Limited | | 1962 |
| Martin Fisher & Co Ltd | Professional & scientific | 2012 |
| Martin James Medical Limited | Health & social care | 1988 |
| Martins Court Management Co. Limited | Households | 1990 |
| Marzipan Hair Limited | Other services | 2019 |
| MAS Ambos Limited | Construction | 2025 |
| MAS Builders (SW) Ltd | Construction | 2019 |
| Maslen Holidays Ltd | Hospitality | 2024 |
| Mason Brewing Co Ltd | Manufacturing | 2023 |
| Mass Ventures Ltd | Real estate | 2025 |
| Massala Tandoori Limited | Hospitality | 2016 |
| Matt Gunn Commercial LLP | | 2021 |
| Matthew Buchan Clinical Coding Ltd | Information & communication | 2021 |
| Matthew J Property Ltd | Real estate | 2023 |
| Matthew Trevail Limited | Construction | 2016 |
| Mavi's Retail Limited | Wholesale & retail | 2009 |
| Mavis Homes Ltd | Real estate | 2019 |
| Mawgan Porth Golf Club Limited | Arts & recreation | 2004 |
| Mawnan Smith Management Company Limited | Households | 2021 |
| MAX Crax BAX Ltd | Health & social care | 2022 |
| MAY Whetter & Grose Limited | Extraterritorial | 2000 |
| Maynes Garage Redruth Limited | Wholesale & retail | 2025 |
| Maynes Garage Services Limited | Wholesale & retail | 2017 |
| Maysen Limited | Real estate | 2023 |
| MBC Dental Limited | Health & social care | 2023 |
| Mbnet Solutions Limited | Information & communication | 2010 |
| Mcgoad Limited | Real estate | 2020 |
| Mcguinness Medical Services Limited | Health & social care | 2013 |
| Mcintosh Properties Ltd | Real estate | 2008 |
| Mclanraysterlin Ltd | Real estate | 2026 |
| MD Dental Care Limited | Health & social care | 2009 |
| Mdelta Limited | Manufacturing | 2017 |
| MDS Leisure (Cornwall) Limited | Arts & recreation | 2015 |
| Meadow Cat Hotel Limited | Administrative & support | 2013 |
| Meadow Pathways Wellbeing and Education Cornwall Ltd | Education | 2025 |
| MED Healthcare and Aesthetics Ltd | Health & social care | 2026 |
| Medfacials Limited | Health & social care | 2020 |
| Media Law Consultancy Limited | Extraterritorial | 2009 |
| Medical Admin Cornwall Limited | Administrative & support | 2026 |
| Mediclock Devices Limited | Wholesale & retail | 2013 |
| Medro Limited | Extraterritorial | 2019 |
| Meiloci Limited | Professional & scientific | 2012 |
| MEL Richardson Consultancy Ltd | Professional & scientific | 2017 |
| Meladore Developments Limited | Construction | 2023 |
| Melin Drive Residents Management Company Limited | Households | 2020 |
| Melinsey Cafe Ltd | Health & social care | 2025 |
| Mellingey Fields Management Company Limited | Households | 2014 |
| Mellingey Valley Management Company Limited | Real estate | 2019 |
| Mellingey Woods Ltd | Households | 2021 |
| Melodie Art Class Ltd | Professional & scientific | 2020 |
| Memos Lounge Bar Ltd | Hospitality | 2026 |
| Menda Construction Limited | Construction | 2016 |
| Meneage Street Surgery Healthcare Limited | Health & social care | 2023 |
| Merrills Johnson Limited | Professional & scientific | 2014 |
| Merrin Meadow Management Company Limited | Households | 2020 |
| Mesh-Wright Ltd | Professional & scientific | 2026 |
| Mesology Limited | Information & communication | 2023 |
| Mesology Network CIC | Financial services | 2025 |
| Metal Surgery Ltd | Manufacturing | 2021 |
| Metmasters Limited | Professional & scientific | 2018 |
| Metro Living Properties Ltd | Real estate | 2026 |
| Meva FC Limited | Hospitality | 2026 |
| MEWS2 Ltd | Construction | 2024 |
| Mewsogen Ltd | Construction | 2024 |
| Mi-Grains Limited | Wholesale & retail | 2010 |
| Michael John Cygan Limited | Extraterritorial | 2025 |
| Microcomms Holdings Limited | Information & communication | 2003 |
| Microcomms Professional Services Limited | Information & communication | 2005 |
| MID Cornwall Design Ltd | Construction | 2006 |
| MID Cornwall FC Ltd | Hospitality | 2025 |
| MID Cornwall Heating Limited | Construction | 2015 |
| MID Cornwall Speech and Language Therapy Limited | Public administration | 2025 |
| Midascheck Limited | Professional & scientific | 1985 |
| Middle Hill Estates Limited | Real estate | 1968 |