| M Stogiera Ltd | Health & social care | 2016 |
| M Tait Joinery Services Ltd | Construction | 2026 |
| M Tech NI Group Ltd | Manufacturing | 2026 |
| M Transformer Ltd | Health & social care | 2021 |
| M W Fresh Foods Limited | Wholesale & retail | 2000 |
| M Wilson Roofing Contractors Limited | Construction | 2019 |
| M&A Ashton Ltd | Hospitality | 2022 |
| M&M Supply Ltd | Wholesale & retail | 2026 |
| M&R Facilities Management Ltd | Construction | 2020 |
| M&U Education and Consulting Ltd | Education | 2024 |
| M. N. GAS Services Limited | Construction | 2011 |
| M.A Locums NE Ltd | Wholesale & retail | 2022 |
| M.A.D Communications Limited | Information & communication | 2013 |
| M.A.R.L. Homes Ltd | Construction | 2018 |
| M.E.E. Catering Limited | Hospitality | 2013 |
| M.H.Southern & Company Limited | Manufacturing | 1949 |
| M.R.E Corp Ltd | Health & social care | 2025 |
| M.S.D NE Ltd | Hospitality | 2019 |
| M3S Orthopaedic Services Private Limited | Health & social care | 2014 |
| M4D Endoscopy Limited | Health & social care | 2025 |
| Ma&Nl Investment Limited | Real estate | 2020 |
| MAC Jointing Ltd | Construction | 2025 |
| MAC Plans Limited | Professional & scientific | 2005 |
| Machinery Services North East Limited | Manufacturing | 2014 |
| Mackem Merch Limited | Wholesale & retail | 2026 |
| Macklin Property Limited | Real estate | 2013 |
| Maclen UK Limited | Construction | 2017 |
| Madras Central Ltd | Hospitality | 2025 |
| Maggs Developments Ltd | Real estate | 2025 |
| Magic & Mayhem Ltd | Arts & recreation | 2017 |
| Magic Hand Carwash (Concord) Ltd | Other services | 2020 |
| Magna Construction I Ltd | Construction | 2021 |
| Magpie Sports Limited | Other services | 2014 |
| Magpies Chippy Ltd | Hospitality | 2025 |
| Magpies Fish Bar Ltd | Hospitality | 2026 |
| Maguires Foods Ltd | Hospitality | 2021 |
| Maguires Residential Ltd | Real estate | 2017 |
| Mahfuz Properties Ltd | Real estate | 2025 |
| Mahmoud Abuawwad Ltd | Health & social care | 2026 |
| Maiden Heworth Ltd | Construction | 2017 |
| Main Fitting Ltd | Construction | 2025 |
| Maino Engineering Limited | Construction | 2014 |
| Mains Building & Maintenance Ltd | Construction | 2018 |
| Make My Day Events Limited | Arts & recreation | 2013 |
| Makerspace Ltd | Other services | 2011 |
| Makwood Properties Ltd | Real estate | 2021 |
| Malik and S Ltd | Real estate | 2020 |
| Mallaghan Optometry Ltd | Health & social care | 2022 |
| Malo Developments Limited | Real estate | 2025 |
| Malones Electricals Group Limited | Administrative & support | 2008 |
| Malones Property Services Ltd | Construction | 2010 |
| Malt Bake Limited | Hospitality | 2019 |
| Mammoth Site Investigations Ltd | Construction | 2022 |
| Manchester Surgical Services Limited | Administrative & support | 2009 |
| Mango Dental Technologies Limited | Manufacturing | 2022 |
| Mantra Fashion Ltd | Wholesale & retail | 2024 |
| Maple House School Limited | Education | 2023 |
| Marbridge Investments Ltd | Real estate | 2025 |
| Marchese Brothers Ltd | Hospitality | 2024 |
| Marcus North Wines Limited | Wholesale & retail | 2014 |
| Margy & Sons Offshore Services Ltd | Other services | 2014 |
| Mariana Ventures Ltd | Real estate | 2020 |
| Marina Consultancy Ltd | Health & social care | 2017 |
| Marindot Global Services Limited | Wholesale & retail | 2023 |
| Marjan NE Ltd | Wholesale & retail | 2017 |
| Mark Forshaw Building Services Ltd | Construction | 2025 |
| Mark Johnston Flooring Limited | Wholesale & retail | 2015 |
| Mark R Ltd | Construction | 2024 |
| Mark Toney Holdings Limited | Manufacturing | 2024 |
| Marketplace Coffee Limited | Hospitality | 2026 |
| Marketspace Coffee Ltd | Hospitality | 2023 |
| Marlborough Holdings Limited | Professional & scientific | 2023 |
| Marlborough Ventures Limited | Real estate | 2018 |
| Marley Developments (UK & IRE) Ltd | Financial services | 2024 |
| Marley Homes (Ryton) Ltd | Construction | 2024 |
| Marmalade Kids Limited | Extraterritorial | 2016 |
| Marrons Mechanical Engineering Limited | Construction | 2019 |
| Marshal's of Washington Ltd | Hospitality | 2025 |
| Marshall & Co Trading Limited | Wholesale & retail | 2026 |
| Marshall Holdings (NE) Ltd | Financial services | 2023 |
| Marshalls Express Ltd | Hospitality | 2024 |
| Marshalls the Bakers Limited | Wholesale & retail | 1946 |
| Martang Property Ltd | Real estate | 2019 |
| Martynow Ltd | Health & social care | 2024 |
| MAS Consultancy & Services Ltd | Administrative & support | 2022 |
| Masbia Homes Ltd | Real estate | 2025 |
| Mash Burger Limited | Hospitality | 2023 |
| Mashkeh Ltd | Extraterritorial | 2011 |
| Maskhouse UK Limited | Wholesale & retail | 2015 |
| Maskhouse Wholesale Limited | Wholesale & retail | 2016 |
| Masonry Solutions Building and Construction Ltd | Construction | 2026 |
| Masons of Newcastle Ltd | Real estate | 2021 |
| Massy Enterprises Ltd | Wholesale & retail | 2022 |
| MASTERTECHIE11 Limited | Manufacturing | 2025 |
| Masterworks Studio Ltd | Professional & scientific | 2026 |
| Mastiff Engineering Ltd | Administrative & support | 2014 |
| Matchurban | Real estate | 1990 |
| Matrix Products Limited | Manufacturing | 1999 |
| Matt Orzel UK Consultancy Limited | Information & communication | 2018 |
| Mattamedia Ltd | Manufacturing | 2018 |