| M&R's Windows Ltd | Construction | 2025 |
| M&S and Sons Motors Limited | Wholesale & retail | 2018 |
| M. Burgess Carpet Services Limited | Wholesale & retail | 2002 |
| M. Conday Plumbing & Heating Ltd | Construction | 2019 |
| M.A.N: Culture CIC | Other services | 2024 |
| M.B.R. Pipeline and Welding Services Limited | Wholesale & retail | 1987 |
| M98 Investments Limited | Financial services | 2021 |
| MA & CLE White Ltd | Construction | 2022 |
| MA Pierce Group Limited | Financial services | 2025 |
| Ma-Ka Bakery Ltd | Manufacturing | 2023 |
| Maarer - Maritime Archaeological Archive Repository and Educational Resource CIC | Arts & recreation | 2025 |
| MAB Car Sales Ltd | Extraterritorial | 2021 |
| Mabel Kitchen Ltd | Hospitality | 2026 |
| Mabil Ltd | Other services | 2011 |
| MAC BOT Enterprise Ltd | Information & communication | 2024 |
| Macdonald Macphee Developments Limited | Wholesale & retail | 2002 |
| Machil Ltd | Wholesale & retail | 2026 |
| Machinemax Pro Limited | Wholesale & retail | 2025 |
| Mackenzie Group Holdings Ltd | Financial services | 2025 |
| Mackiefam Investments Ltd | Real estate | 2026 |
| Mackintosh Martin Gardening Limited | Administrative & support | 2023 |
| Macleod Motor Co Ltd | Wholesale & retail | 2023 |
| Macpherson Motorcycles Ltd | Wholesale & retail | 2021 |
| Macs Legal Services Ltd | Professional & scientific | 2016 |
| MAD (Plymouth) Holdings Ltd | Financial services | 2020 |
| MAD (Plymouth) Ltd | Information & communication | 1993 |
| MAD Financial Media Limited | Information & communication | 2020 |
| MAD for IT Pubs Ltd | Hospitality | 2024 |
| Made Developments (SW) Ltd | Real estate | 2026 |
| Made Snappy 360 Limited | Information & communication | 2021 |
| Made Snappy Limited | Information & communication | 2018 |
| Made With Maturity Limited | Information & communication | 2015 |
| Madge Consulting Ltd | Professional & scientific | 2018 |
| Madison House Management (Plymouth) Company Limited | Real estate | 2006 |
| Mady's Holistic Therapy Ltd | Other services | 2025 |
| Maelstrom Boats Limited | Wholesale & retail | 2026 |
| MAG DEV Ltd | Information & communication | 2023 |
| MAG Developments SW Limited | Construction | 2022 |
| MAG Shopfitting Limited | Construction | 2004 |
| Magenta Social Work Ltd | Health & social care | 2021 |
| Maggie's Sewing Box Ltd | Wholesale & retail | 2022 |
| Magic Beans Developments Limited | Real estate | 2022 |
| Magic Scarves Ltd | Wholesale & retail | 2020 |
| Magicka Interactive Limited | Information & communication | 2002 |
| Magily Limited | Real estate | 1994 |
| Magnetic Matrix Ltd | Information & communication | 2025 |
| MAGPIESNEST925 Limited | Manufacturing | 2021 |
| Magrow Ltd | Real estate | 2026 |
| Mahkola Haven Ltd | Wholesale & retail | 2026 |
| MAID2CLEAN (Plymouth) Ltd | Administrative & support | 2020 |
| MAIL2SEND Ltd | Transport & logistics | 2015 |
| Main Event (UK) Ltd | Hospitality | 2013 |
| Main's Roofing & Facilities Limited | Construction | 2009 |
| Mainies Ltd | Hospitality | 2018 |
| Mainly Kitchens Ltd | Manufacturing | 2005 |
| Maison A.E.L. Limited | Real estate | 1944 |
| Maison Elysian DE Soirée Co. Ltd | Hospitality | 2025 |
| Maisonette Management Limited | Households | 1986 |
| Maize Cleaning Solutions Limited | Administrative & support | 2025 |
| Majesty Property Services Ltd | Real estate | 2023 |
| Majestyapartments Ltd | Real estate | 2019 |
| Make a Difference Project CIC | Education | 2026 |
| Make a Dream Publishing Limited | Information & communication | 2010 |
| Make Data Sense Ltd | Information & communication | 2023 |
| Maktop Ltd | Health & social care | 2019 |
| MAL Research and Development Limited | Professional & scientific | 2012 |
| Malar Service Ltd | Wholesale & retail | 2018 |
| Malhan Limited | Wholesale & retail | 2024 |
| Maliphant Apartments RTM Company Limited | Households | 2024 |
| Malmo Barbers (SW) Ltd | Other services | 2024 |
| Malthouse Court Management Limited | Households | 2012 |
| Mama Africa (SW) Ltd | Wholesale & retail | 2024 |
| Mammoth Roofing Limited | Wholesale & retail | 2020 |
| Manadon Cars Ltd | Transport & logistics | 2026 |
| Manadon Court Residents Association Limited | Real estate | 1981 |
| Manadon Park (Plymouth) Management Company Limited | Households | 2003 |
| Manageair Ltd | Real estate | 2021 |
| Manamen Limited | Wholesale & retail | 2011 |
| Mancuso Building Ltd | Other services | 2025 |
| Mandan Ltd | Financial services | 2025 |
| Mandh Filmhouse Ltd | Information & communication | 2022 |
| Mangotsfield Pre-School Limited | Education | 2010 |
| Maniam & Sons Ltd | Wholesale & retail | 2020 |
| Manifest Arts CIC | Arts & recreation | 2024 |
| Mannamead Cars Ltd | Wholesale & retail | 2005 |
| Mannamead Court Management Company Ltd | Households | 2003 |
| Mannamead Express Ltd | Administrative & support | 2026 |
| Mannamead News Ltd | Wholesale & retail | 2011 |
| Mannaz MMA Ltd | Education | 2024 |
| Mannell Limited | Professional & scientific | 2024 |
| Manning & Company (South West) Limited | Professional & scientific | 1995 |
| Manole Artisan Ltd | Manufacturing | 2025 |
| Manor Acquisitions Ltd | Wholesale & retail | 2020 |
| Manor Drive Investments Limited | Financial services | 2012 |
| Manor Garage Plymouth Limited | Wholesale & retail | 2015 |
| Manor Land Limited | Other services | 2014 |
| Manor Mills Management Company Limited | Households | 2023 |
| Manor Street Galleries Limited | Arts & recreation | 2023 |
| Manor Street Garage Ltd | Wholesale & retail | 2024 |
| Mansfield Building Services Ltd | Construction | 2019 |