| Marsh Barton Security Services Limited | Extraterritorial | 2012 |
| Marsh Barton Social Club Company Limited | Arts & recreation | 1964 |
| Marsh Garages Limited | Wholesale & retail | 2001 |
| Marsh Green Associates Ltd | Construction | 2019 |
| Marsh Holdings Limited | Professional & scientific | 2008 |
| Marsh House (Alphington Road Exeter) (NO 2) Management Company Limited | Hospitality | 2011 |
| Marsh Motorcycles Limited | Wholesale & retail | 2008 |
| Marsh Tyres & Autos Limited | Wholesale & retail | 2019 |
| Marsh Tyres & Autos Tiverton Limited | Wholesale & retail | 2019 |
| Marshall Pomeroy Limited | Real estate | 2025 |
| Marshmallow Cactus Ltd | Other services | 2024 |
| Martest Ltd | Professional & scientific | 2023 |
| Martin and Phillips Building Services Ltd | Construction | 2015 |
| Martin Diment Ltd | Professional & scientific | 2019 |
| Martin Diplock Ltd | Real estate | 2010 |
| Martingate Developments Limited | Construction | 2023 |
| Martins Amusements Limited | Arts & recreation | 2003 |
| Martins Dairy of Looe Ltd | Manufacturing | 2024 |
| Martinsfield Farm Enterprises LLP | | 2016 |
| Martyn LEE Haulage Limited | Transport & logistics | 2002 |
| Martyr Merchants Ltd | Wholesale & retail | 2017 |
| Masala Lounge Exeter Ltd | Hospitality | 2025 |
| Mascut Limited | Other services | 2025 |
| Mason and England Holdings Limited | Manufacturing | 2025 |
| Massage and Wellbeing Limited | Health & social care | 2023 |
| Massco Limited | Real estate | 2020 |
| Masscommunication Limited | Administrative & support | 2010 |
| Masswick Limited | Administrative & support | 1996 |
| Master Barber SW Limited | Other services | 2026 |
| Master Builders (Holsworthy) Limited | Construction | 2019 |
| Master Builders (South West) Limited | Construction | 2019 |
| Master Roofing & Flat Roofing Ltd | Construction | 2026 |
| Masterclean (SW) Limited | Administrative & support | 1998 |
| Mata Hosting Limited | Real estate | 2023 |
| Match My Venue Limited | Wholesale & retail | 2024 |
| Matchbox Sauna Ltd | Other services | 2025 |
| Material MUM Designs Limited | Manufacturing | 2025 |
| Matford Arable Systems (Holdings) Limited | Financial services | 2014 |
| Matford Arable Systems Limited | Wholesale & retail | 1991 |
| Matford Dental Clinic Limited | Health & social care | 2009 |
| Matford Mews Management Company Limited | Households | 1988 |
| Matford Property Limited | Real estate | 2014 |
| Mathias & Partners Limited | Real estate | 2012 |
| Matilda Blue Limited | Real estate | 2016 |
| Matrix Engineering Ltd | Construction | 2007 |
| Matse Builders Ltd | Construction | 2012 |
| Matse Limited | Wholesale & retail | 2010 |
| Matter Brew Ltd | Information & communication | 2024 |
| Matthew J Recruitment Ltd | Administrative & support | 2026 |
| Matthew Moran Photography Ltd | Professional & scientific | 2026 |
| Matthew Townshend Productions Limited | Arts & recreation | 2005 |
| Matthew Way Ltd | Other services | 2016 |
| Matthews Court Management Limited | Households | 1984 |
| Maude Morrison Consulting Limited | Professional & scientific | 2021 |
| Maunder Consulting Limited | Administrative & support | 2023 |
| Mavlink Ltd | Transport & logistics | 2026 |
| MAX Barron Ltd | Professional & scientific | 2021 |
| MAX Langmaid Motorsport Ltd | Wholesale & retail | 2020 |
| Maxa Services Limited | Professional & scientific | 2025 |
| Maximum Consulting Ltd | Information & communication | 2024 |
| Maximum FUN Cornwall Limited | Arts & recreation | 2001 |
| Maximum FUN Devon Limited | Arts & recreation | 2011 |
| Maximum FUN Holdings Limited | Administrative & support | 2011 |
| MAY & Mckay Property Investment Limited | Real estate | 2023 |
| MAY Inc Limited | Education | 2023 |
| Maybe Agency Limited | Professional & scientific | 2025 |
| Maycom Ltd | Wholesale & retail | 2016 |
| Mayflower Caravan Transport Holding Co Ltd | Transport & logistics | 2024 |
| Mayflower E-Commerce Limited | Wholesale & retail | 2023 |
| Mayflower Investment Partners Ltd | Financial services | 2021 |
| Mayflower Mortgage and Finance Ltd | Financial services | 2020 |
| Mayflower Transport Limited | Transport & logistics | 1999 |
| Mayfort Limited | Real estate | 2026 |
| Mayhaven Healthcare Limited | Health & social care | 2007 |
| Mazala HUT Limited | Hospitality | 2025 |
| Mazumder (Exeter) Ltd | Hospitality | 2019 |
| MB Accounting and Business Solutions Ltd | Professional & scientific | 2022 |
| MB Aviation Composite Services Ltd | Professional & scientific | 2022 |
| MB Marine Ltd | Transport & logistics | 2016 |
| MB Mednest Ltd | Health & social care | 2025 |
| Mbassociates SW Ltd | Professional & scientific | 2012 |
| MBM Group Services Limited | Administrative & support | 2015 |
| MC Carpentry and Joinery (SW) Limited | Manufacturing | 2017 |
| MC Exeter Limited | Administrative & support | 2005 |
| MC Living Ltd | Real estate | 2019 |
| MC Services AG Limited | Administrative & support | 2016 |
| MC2 Property Group Ltd. | Real estate | 2017 |
| Mcconnell Fire and Security Ltd | Construction | 2021 |
| Mccox Ltd | Real estate | 2016 |
| Mcdiarmid-Hall Clinic Limited | Health & social care | 2002 |
| MCF Group Limited | Financial services | 2021 |
| Mcgauley Holdings Ltd | Real estate | 2021 |
| Mcgrewal Solutions Ltd | Information & communication | 2024 |
| Mcguirk & Jepson Limited | Information & communication | 2025 |
| MCH Land Solutions Ltd | Construction | 2026 |
| MCH Properties South West Ltd | Real estate | 2018 |
| Mchugh & Co Limited | Other services | 1987 |
| Mckay Woodwork Ltd | Construction | 2012 |
| Mckenzie Motorworks Ltd | Wholesale & retail | 2020 |
| Mclainesholdings Ltd | Financial services | 2019 |