| Magichandspg Ltd | Wholesale & retail | 2025 |
| Magna ES UK Limited | Professional & scientific | 2013 |
| Magpie Fencing Limited | Administrative & support | 2020 |
| MAM Houghton Ltd | Hospitality | 2024 |
| Mama Lou's Lettings Ltd | Real estate | 2026 |
| Manchester Accident Repair Centre Limited | Wholesale & retail | 2005 |
| Manlas Ltd | Information & communication | 2025 |
| Manor House Leisure Limited | Arts & recreation | 1987 |
| Maple Street Light Limited | Real estate | 2014 |
| Maple Tree and Forestry Services Limited | Agriculture & fishing | 2026 |
| Mapleside Residential Limited | Real estate | 2023 |
| Mariners (UK) Limited | Hospitality | 2009 |
| Mastech Inspections Ltd | Professional & scientific | 2024 |
| Matrix Construction NE Ltd | Construction | 2026 |
| Matthew O'Donnell Limited | Other services | 2026 |
| Mattywilliamsoncoaching Ltd | Health & social care | 2025 |
| MAX Recycle (UK) Limited | Water & waste | 2008 |
| Mayoori Investments Ltd | Real estate | 2020 |
| Mazkenz Services Limited | Water & waste | 2021 |
| MB Grab a Load Ltd | Transport & logistics | 2019 |
| MC Buckley Consulting Limited | Professional & scientific | 2024 |
| Mccarron Projects Limited | Professional & scientific | 2024 |
| Mcdonald PA Services Limited | Professional & scientific | 2017 |
| Mcghin Power Solutions Ltd | Construction | 2025 |
| Mcleod Quality Services Ltd | Professional & scientific | 2016 |
| MCW and Partners Ltd | Professional & scientific | 2025 |
| MD Engineering Services (UK) Limited | Construction | 2007 |
| Media Spin Ltd | Financial services | 2011 |
| Mediuz Limited | Health & social care | 2025 |
| Meek Steelfab Limited | Wholesale & retail | 1983 |
| Menorca Villa Holidays (Property Letting) Limited | Real estate | 2001 |
| Merlin Leisure NE Ltd | Hospitality | 2014 |
| Metalock International Association Limited | Professional & scientific | 1953 |
| MGS Maddison GAS Solutions Ltd | Construction | 2022 |
| MHC Skin Clinic Ltd | Health & social care | 2021 |
| MHR Private Limited | Wholesale & retail | 2025 |
| Mickleton Properties Ltd | Real estate | 2026 |
| Microbritt Ltd | Professional & scientific | 2021 |
| Midas Homes & Lettings Ltd | Real estate | 2020 |
| Middlesex Interiors Limited | Construction | 2016 |
| MIL HOR Ltd | Wholesale & retail | 2025 |
| Milbank Arms (Well) Limited | Hospitality | 1996 |
| Millers Food to Go Ltd | Hospitality | 2025 |
| Millfield Community Collective CIC | Arts & recreation | 2024 |
| Milmac Limited | Construction | 2016 |
| Missy's Mutts Dog Grooming Ltd | Other services | 2023 |
| Mitten Publishing Limited | Information & communication | 2014 |
| MJS Sales Limited | Professional & scientific | 2025 |
| MK Windfarm Limited | Energy | 2004 |
| MLF Tech Support Limited | Information & communication | 2025 |
| MN Food Hub Ltd | Hospitality | 2026 |
| Modus Staffing Ltd | Administrative & support | 2025 |
| Moffett & March Limited | Construction | 2001 |
| Mogis 2023 Ltd | Hospitality | 2023 |
| Monday's Child Cleaning Services Ltd | Administrative & support | 2023 |
| Mondo NE Limited | Wholesale & retail | 2025 |
| Montgomery Materials Management Ltd | Professional & scientific | 2010 |
| Monument Doors Ltd | Construction | 2025 |
| Monument Public House Penshaw Ltd Ltd | Hospitality | 2026 |
| Monument Roofing Ltd | Construction | 2026 |
| Monument Scaffold North East Ltd | Construction | 2025 |
| MOO Rope Works Ltd | Manufacturing | 2024 |
| Mood ( Bedlington ) Ltd | Professional & scientific | 2024 |
| Moralee & Co NE Ltd | Other services | 2023 |
| Morley Capital Apac Ltd | Financial services | 2025 |
| Morley Capital Ltd | Financial services | 2023 |
| Morphcryst Consulting Limited | Professional & scientific | 2025 |
| Morrell Financial Management Limited | Financial services | 2012 |
| Morrell Will Services Ltd | Professional & scientific | 2021 |
| Mortimer & Mortimer Ltd | Health & social care | 2018 |
| Morton Grange Partnership LLP | | 2025 |
| Mosside RTM Company Limited | Real estate | 2012 |
| Mountfield Quality Products Limited | Manufacturing | 1996 |
| MP Holdco Limited | Administrative & support | 2017 |
| MRS Brightside Travel Ltd | Administrative & support | 2024 |
| MS Property Management NE Ltd | Real estate | 2019 |
| MSC Enterprise (NE) Limited | Wholesale & retail | 2022 |
| MSG Hodgson Logistics Ltd | Transport & logistics | 2025 |
| MT Engineering & Hydraulic Services Ltd | Manufacturing | 2022 |
| MT Engineering Group Ltd | Financial services | 2025 |
| Mtacs Ltd | Professional & scientific | 2012 |
| MTS Distribution Limited | Households | 2005 |
| Mudwasher Ltd | Wholesale & retail | 2025 |
| Mulberry Park NE Community Interest Company | Health & social care | 2026 |
| Mulvaney Estate Management Ltd | Real estate | 2021 |
| Munro Contractors Limited | Construction | 2024 |
| Muscletone Gym and Fitness Community Interest Company | Other services | 2017 |
| Mwspecialists Ltd | Manufacturing | 2023 |
| My Civil Engineers Ltd | Construction | 2021 |
| My Civil Holdings Ltd | Financial services | 2026 |
| My Stock Flow Limited | Information & communication | 2025 |
| Myfi Limited | Financial services | 2013 |
| Mykindaearth Ltd | Wholesale & retail | 2019 |
| Myss Sunderland Limited | Hospitality | 2024 |
| N S Gaming Limited | Arts & recreation | 2007 |
| N.E. Truck Spares Limited | Wholesale & retail | 1974 |
| Najafshop Ltd | Wholesale & retail | 2025 |
| Napier Energy Services Ltd | Extraterritorial | 2024 |
| NE1 City Studios & Apartments Ltd | Real estate | 2024 |
| Nells Haulage Limited | Transport & logistics | 2009 |