| M I Developments Limited | Construction | 2022 |
| M L G Electrical Contracting Limited | Construction | 2018 |
| M Martin Decorators North East Limited | Construction | 2021 |
| M R Vape & Candy Shop Limited | Wholesale & retail | 2026 |
| M&D Family Transport Limited | Transport & logistics | 2021 |
| M&M Cladding Ltd | Construction | 2020 |
| M&M Mart Limited | Transport & logistics | 2024 |
| M&M Servicez Ltd | Wholesale & retail | 2024 |
| M&R Property North East Ltd | Real estate | 2025 |
| M&S Catering Limited | Hospitality | 2025 |
| M&S Mart Limited | Wholesale & retail | 2024 |
| M&S Property Lets Ltd | Real estate | 2024 |
| M-Eat Fresh Ltd | Hospitality | 2025 |
| M. Lowes Properties Limited | Real estate | 2011 |
| M.E.M. Engineering (UK) Limited | Professional & scientific | 2000 |
| M.S.N Secure Services Ltd | Financial services | 2023 |
| M40 Trains Limited | Transport & logistics | 1994 |
| MAC Catering Ltd | Hospitality | 2024 |
| Macdonald Electrical Services (MES) Ltd | Construction | 2025 |
| Macey Property Company Ltd | Real estate | 2025 |
| Mackay Int’L Limited | Hospitality | 2025 |
| Mackem Media Limited | Information & communication | 2023 |
| Maclav Limited | Education | 2017 |
| Macleod's (North East) Ltd | Administrative & support | 2021 |
| MAD About Renovation Ltd | Real estate | 2018 |
| MAD About Renting Limited | Real estate | 2022 |
| MAD Clean Ltd | Extraterritorial | 2024 |
| Madam Media Limited | Information & communication | 2019 |
| Madden Enterprises Ltd | Real estate | 2025 |
| Madrive Computing Limited | Information & communication | 1998 |
| Magic Fades Barbers Ltd | Other services | 2026 |
| Magic Scissors 2 UK Limited | Other services | 2022 |
| Magic Touch Y Beauty Ltd | Health & social care | 2024 |
| Magicpot 9JA Ltd | Hospitality | 2025 |
| Magnesian Limited | Professional & scientific | 2021 |
| Maha Dulay Limited | Wholesale & retail | 2014 |
| Maineside Developments Limited | Wholesale & retail | 1998 |
| Mainstreet Sparkle Ltd | Manufacturing | 2025 |
| Maintenance Magic Limited | Other services | 2019 |
| Maison Vides Limited | Real estate | 2022 |
| Makaveli Holdings Ltd | Real estate | 2018 |
| Makem Palace Ltd | Hospitality | 2019 |
| Makruma Ltd | Wholesale & retail | 2022 |
| Malabar Seaburn Ltd | Hospitality | 2026 |
| Malazaar Ltd | Wholesale & retail | 2021 |
| Malhaar Limited | Wholesale & retail | 2019 |
| Malthouse HR Solutions Limited | Information & communication | 2018 |
| Maltrab Limited | Wholesale & retail | 2020 |
| Mama Italia Limited | Hospitality | 2022 |
| Mama's Delivery Limited | Hospitality | 2014 |
| Mama's Italian Kitchen Limited | Hospitality | 2010 |
| Mamamia P Ltd | Hospitality | 2024 |
| Mama’S Delight Food and More Limited | Manufacturing | 2026 |
| Manatee Limited | Other services | 2012 |
| Manberg Projects Ltd | Arts & recreation | 2021 |
| Manex Consultants Ltd. | Professional & scientific | 2018 |
| Manfield Wealth Management Limited | Financial services | 2019 |
| Mangat Properties Investment Ltd | Real estate | 2024 |
| Mangostack Ltd | Information & communication | 2026 |
| Manhattan 2GO Ltd | Hospitality | 2026 |
| Mann Stores ( Sunderland ) Ltd | Wholesale & retail | 2020 |
| Mann Wholesale Ltd | Wholesale & retail | 2023 |
| Mannerwild Limited | Manufacturing | 1998 |
| Mannyl Ltd | Health & social care | 2021 |
| Manor Fold (Walkden) Management Company Limited | Households | 2007 |
| Manor House Funeral Directors Ltd | Other services | 2025 |
| Mantle & Partners Limited | Financial services | 1999 |
| Manufacturing Data Consultants Limited | Information & communication | 2007 |
| Manzur Housing II Limited | Real estate | 2025 |
| MAP Property NE Limited | Real estate | 2026 |
| Maplegreen Energyfarm Limited | Energy | 2024 |
| Maps (NE) Ltd | Real estate | 2019 |
| Marand Pizza Ltd | Hospitality | 2025 |
| Marc 85 Ltd | Hospitality | 2025 |
| Marcean Properties Limited | Real estate | 2024 |
| Marcmac Ltd | Transport & logistics | 2026 |
| Marengo Estates Ltd | Real estate | 2020 |
| Marikal Design and Build Limited | Administrative & support | 2016 |
| Marikal Limited | Construction | 2013 |
| Marine House Gym Ltd | Arts & recreation | 2025 |
| Mario Barbers Sunderland Ltd | Other services | 2023 |
| Mario Pizza Ltd | Hospitality | 2024 |
| Maritime Buildings RTM Company Limited | Households | 2020 |
| Maritime Meeting Rooms CIC | Arts & recreation | 2019 |
| Mariya Care Limited | Health & social care | 2017 |
| Mark Anderson HSE Solutions Ltd | Construction | 2025 |
| Mark C Services Ltd | Other services | 2025 |
| Mark Jacobs Wealth Management Limited | Financial services | 2014 |
| Mark Mcnally Wealth Management Ltd | Financial services | 2013 |
| Marker UK Limited | Professional & scientific | 2016 |
| Marketing of Things Ltd | Professional & scientific | 2023 |
| Marland Fabrications Limited | Manufacturing | 1995 |
| Marley Building and Joinery Ltd | Construction | 2022 |
| Marley Roofcare Ltd | Construction | 2015 |
| Marmaris Barbershop Solution Limited | Other services | 2025 |
| Marmite Ltd | Other services | 2021 |
| Marriott Communications & PR Limited | Professional & scientific | 2022 |
| Marsen Limited | Administrative & support | 2007 |
| Marson Investments Limited | Real estate | 2016 |
| Marsool Ltd | Transport & logistics | 2024 |