| M&D Restaurant Ltd | Hospitality | 2023 |
| M. Wilson Plumbing & Heating Limited | Construction | 1999 |
| M.G.Wilson Electrical Ltd | Construction | 2014 |
| M4C Ltd | Professional & scientific | 2018 |
| Mace Estates Ltd | Real estate | 2025 |
| Machander & Wilson Digital Consultants Limited | Professional & scientific | 2025 |
| Maier Care Limited | Health & social care | 2003 |
| Makepeace Forestry & Landscaping Limited | Agriculture & fishing | 2023 |
| Malco Tyre Specialists Ltd | Wholesale & retail | 2015 |
| Malshop Ltd | Wholesale & retail | 2025 |
| Marble Stories Ltd | Construction | 2024 |
| Mari Hannah Ltd | Arts & recreation | 2014 |
| Maria Richardson Coaching and Consulting Ltd | Professional & scientific | 2021 |
| Maritime Holdings Limited | Professional & scientific | 1988 |
| Mark Crow Catering North Tyne Limited | Hospitality | 2025 |
| Mark Hill Studio Ltd | Professional & scientific | 2014 |
| Market Place Hexham Ltd | Hospitality | 2023 |
| Market Place Limited | Wholesale & retail | 2005 |
| Martonlynn Limited | Wholesale & retail | 1983 |
| Mary's Healthy Weigh Limited | Health & social care | 2017 |
| Masterman Engineering Ltd | Professional & scientific | 2024 |
| Materials in Massed Environment Limited | Professional & scientific | 2022 |
| Matt Clark Limited | Wholesale & retail | 1963 |
| Matt Dechaine Coaching and Development Limited | Education | 2019 |
| Matthew Jansen Legal Translation Ltd | Professional & scientific | 2008 |
| Matthew Kirkby Holdings Limited | Real estate | 2017 |
| Matty Lamb Golf Ltd | Arts & recreation | 2022 |
| Mauchlen Weightman & Elphick Architects LLP | | 2016 |
| Mccluskie Property Hexham Ltd | Real estate | 2025 |
| Mccluskie Property Ltd | Hospitality | 2022 |
| Mcgowan Engineering Developments Limited | Manufacturing | 2019 |
| Mcintosh's Factory Shop Limited | Wholesale & retail | 2001 |
| Mckie Property Holdings Ltd | Real estate | 2026 |
| MCL Development Solutions Ltd | Professional & scientific | 2017 |
| Mclure and Co Ltd | Construction | 2025 |
| Mcpherson Surveying Ltd | Professional & scientific | 2023 |
| Meal Market-Ing Limited | Professional & scientific | 2024 |
| Medical Aesthetics and Wellbeing Ltd | Health & social care | 2016 |
| Meet the 85% Limited | Information & communication | 2023 |
| Melting IT Productions Ltd | Information & communication | 2022 |
| Memorymovies Ltd | Information & communication | 2026 |
| Menopause Medical Hexham LLP | | 2025 |
| Merida Group Limited | Construction | 2016 |
| Meridian Advice Limited | Financial services | 2002 |
| Mewshouse Property Management Ltd | Real estate | 2019 |
| MGF on the Water Limited | Agriculture & fishing | 2020 |
| Mibex Ltd | Professional & scientific | 2017 |
| Milburn Coaches Ltd | Transport & logistics | 2020 |
| Milburn Davies Partnership Ltd | Financial services | 2010 |
| Milburn Planning Limited | Professional & scientific | 2016 |
| Milkside Properties Limited | Professional & scientific | 2017 |
| Mill Flats Limited | Extraterritorial | 2012 |
| Millennium 3 Automotive UK Ltd | Professional & scientific | 2020 |
| Mineral Surveying Associates Ltd | Real estate | 2019 |
| Minerva Northumberland Limited | Arts & recreation | 2002 |
| Minnie Management Ltd | Real estate | 2023 |
| Miscreations Theatre Ltd | Arts & recreation | 2020 |
| MJS Medical Ltd | Health & social care | 2023 |
| MKB Consulting Northern Limited | Professional & scientific | 2025 |
| Molly Selby Eventing Ltd | Agriculture & fishing | 2025 |
| Montari AI Limited | Professional & scientific | 2025 |
| Moon Medical Health Ltd | Health & social care | 2022 |
| Morpeth Business Hub Limited | Real estate | 2025 |
| Morpeth Limited | Administrative & support | 2003 |
| Mosaic Developments Ltd | Real estate | 2022 |
| Mosaic Intelligence Ltd | Information & communication | 2026 |
| Mosaic Partners Ltd | Professional & scientific | 2016 |
| Mosslime Consultants Ltd | Administrative & support | 1999 |
| Mountain Dawn Ltd | Professional & scientific | 2022 |
| Mountain Goat Investments Limited | Real estate | 2020 |
| MRC Forestry Limited | Agriculture & fishing | 2025 |
| Multi Project Support (UK) Ltd | Administrative & support | 1983 |
| Multi Project Support Limited | Administrative & support | 1992 |
| Murphysoft Limited | Information & communication | 1997 |
| Musterfield Poultry Growers Ltd | Agriculture & fishing | 2010 |
| Myhus Ltd | Construction | 2013 |
| N & J Bell Limited | Transport & logistics | 2003 |
| N & N Hindmarsh Limited | Agriculture & fishing | 2014 |
| N K Landscaping North East Ltd | Administrative & support | 2026 |
| N Urwin Design Engineering Ltd | Professional & scientific | 2021 |
| N. G. R. Takeaway Ltd | Hospitality | 2012 |
| National Learning Group Limited | Education | 2016 |
| National Youth Film Academy Limited | Information & communication | 2019 |
| Natural Ability | Hospitality | 2009 |
| NE Car Store Ltd | Wholesale & retail | 2026 |
| Needham Heritage Limited | Professional & scientific | 1996 |
| Nehvyan Ltd | Hospitality | 2017 |
| Neptune Inspection Limited | Professional & scientific | 2015 |
| Neville White Construction Limited | Construction | 2021 |
| Newbase Project Management Limited | Construction | 2016 |
| Newbrough Town Hall | Arts & recreation | 2011 |
| Newbrough Trading Limited | Hospitality | 2011 |
| Newshams Online Marketing Ltd | Professional & scientific | 2012 |
| Newshams Tax Advisers Ltd | Extraterritorial | 2016 |
| Newton and Charlton LLP | | 2016 |
| Newton Barns Ltd | Construction | 2025 |
| Nexgen Building Company Ltd | Construction | 2026 |
| Next-Level Tableau Limited | Professional & scientific | 2025 |
| Nexus Hive Limited | Administrative & support | 2025 |
| Nichkl Limited | Other services | 2009 |