| Mart-Fort Ltd | Wholesale & retail | 2021 |
| Martin Telfer Carpets Limited | Wholesale & retail | 2008 |
| Marwell Investments Limited | Financial services | 2023 |
| Marys Pallian Ltd | Hospitality | 2026 |
| Mason & Forster Limited | Construction | 2011 |
| Massbe Farm Food Limited | Wholesale & retail | 2025 |
| Massimo's Pizza Limited | Hospitality | 2018 |
| Master Key Education Limited | Education | 2024 |
| Master Services Workwear Limited | Wholesale & retail | 2023 |
| Masterpiece by Ndow Ltd | Manufacturing | 2025 |
| Matamba Ltd | Education | 2020 |
| Matchmakers Worldwide Limited | Wholesale & retail | 2004 |
| Matgo Ltd | Manufacturing | 2025 |
| Matis Paris UK Ltd | Wholesale & retail | 2017 |
| Matis UK Products Ltd | Wholesale & retail | 2020 |
| Matlock Wealth Management Limited | Financial services | 2013 |
| Matom Limited | Construction | 2000 |
| Matthew J Potts & Family Ltd | Construction | 2022 |
| Matthews Medicolegal Expert Witness Services Ltd | Public administration | 2021 |
| Mattress Vendor Ltd | Manufacturing | 2023 |
| Maverick Components (UK) Limited | Wholesale & retail | 2010 |
| Mavericks X Everest Ltd | Health & social care | 2025 |
| Mavibs Limited | Wholesale & retail | 2026 |
| MAX Europe Limited | Wholesale & retail | 2005 |
| MAX Plus Developments Ltd | Construction | 2025 |
| MAX Zipper (Europe) Company Limited | Wholesale & retail | 2014 |
| Max's Barberz Ltd | Other services | 2025 |
| Maxipact Healthcare and Global Investments Limited | Wholesale & retail | 2024 |
| Maxw Consult Ltd | Professional & scientific | 2020 |
| MAY Gair Limited | Wholesale & retail | 2026 |
| MAY HO Limited | Hospitality | 2018 |
| Maya Holdings NE Ltd | Real estate | 2021 |
| Mayfair Service Station Limited | Wholesale & retail | 2024 |
| Mayfair Shooting Club Limited | Arts & recreation | 2014 |
| Maygreen Group Ltd | Financial services | 2019 |
| Maygreen Investments Ltd | Real estate | 2016 |
| Maygreen Services Ltd | Real estate | 2019 |
| Maywish Services Ltd | Wholesale & retail | 2026 |
| Mazon Global Limited | Construction | 2025 |
| MB3 Holdings Ltd | Administrative & support | 2023 |
| MBL Properties Ltd | Real estate | 2018 |
| MC Computers Ltd | Information & communication | 2019 |
| MC Properties North East Ltd | Real estate | 2025 |
| MC Retrofit Solutions Ltd | Administrative & support | 2025 |
| Mcarthur Property Limited | Households | 2023 |
| MCC Holdings Limited | Financial services | 2017 |
| MCC Homes Limited | Construction | 2017 |
| MCC Media Limited | Arts & recreation | 2008 |
| MCC11 Ltd | Construction | 2019 |
| Mccabe Bricklaying Ltd | Construction | 2025 |
| Mccarthy’S House Property’S Ltd | Real estate | 2025 |
| Mccormack Care Ltd | Health & social care | 2017 |
| Mccoy's Bakery Limited | Hospitality | 2025 |
| MCG Property Soloutions Limited | Construction | 2018 |
| Mcgeorge Financial Limited | Professional & scientific | 2016 |
| Mciver Retail Limited | Hospitality | 2008 |
| MCK Cleaning Services (NE) Ltd | Administrative & support | 2025 |
| Mckell Holidays and Lettings Ltd | Hospitality | 2024 |
| Mckenzie Bell Ltd | Professional & scientific | 2012 |
| Mckenzie Claims Management Ltd | Professional & scientific | 2015 |
| Mclaughlin Healthcare Ltd | Public administration | 2022 |
| Mcneilly Consulting and Associates Ltd | Professional & scientific | 2016 |
| Mctools Limited | Wholesale & retail | 2013 |
| MCW Property Limited | Real estate | 2014 |
| MD Andrea Ltd | Construction | 2024 |
| MD Digital Business Solutions Limited | Information & communication | 2024 |
| MD Renewable Energy Ltd | Energy | 2023 |
| MD Wind Ltd | Construction | 2025 |
| MDB Marine Limited | Administrative & support | 2013 |
| MDM Marketing Ltd | Professional & scientific | 2021 |
| MDO Electrical Services Ltd | Construction | 2025 |
| MDR Architectural Ltd | Professional & scientific | 2024 |
| Mead 7 Limited | Administrative & support | 2022 |
| Meadowsweet Properties Limited | Real estate | 2025 |
| Meah's Group Limited | Real estate | 2026 |
| Meat in Place (Sunderland) Ltd | Hospitality | 2023 |
| Mechanic AI Limited | Wholesale & retail | 2026 |
| Mechlavish Limited | | 1988 |
| Mectronics UK Ltd. | Administrative & support | 1995 |
| MED Kitchen Wingate Ltd | Hospitality | 2024 |
| Medcoveruk Ltd | Health & social care | 2021 |
| Media Savvy Training Solutions Community Interest Company | Education | 2010 |
| Medichem (Sunderland) Limited | Professional & scientific | 2008 |
| Medichem Limited | Wholesale & retail | 2002 |
| Medicus Healthcare Limited | Health & social care | 2014 |
| Medintu Limited | Information & communication | 2015 |
| Meekol Limited | Construction | 2017 |
| Megator Limited | Manufacturing | 1946 |
| MEH Inspection Limited | Construction | 2020 |
| Mehak Limited | Hospitality | 2018 |
| Mehran Ltd | Wholesale & retail | 2019 |
| Mehraneh Ltd | Hospitality | 2026 |
| Mehrdad Food Ltd | Hospitality | 2024 |
| Mehto Transport Ltd | Transport & logistics | 2023 |
| Melani's Springwell Ltd | Hospitality | 2024 |
| Melbourne Place (NE) Ltd | Hospitality | 2024 |
| Melbourne Spices (Sunderland) Ltd | Hospitality | 2019 |
| Mell Management Ltd | Professional & scientific | 2023 |
| Melos Holdings Limited | Administrative & support | 2025 |
| Memento Funeral Stationery Limited | Manufacturing | 2013 |