| Malnor Maintenance (Southern) Limited | Households | 2014 |
| Malnor Southern Limited | Construction | 1991 |
| Manastra Ltd | Administrative & support | 2012 |
| Mandycoalter HR Ltd | Professional & scientific | 2019 |
| Manhattan Apartments Management Company Limited | Households | 2004 |
| Manners Arms (Belvoir) Limited | Hospitality | 2024 |
| Manners Family Co Limited | Wholesale & retail | 2012 |
| Manor House Capital Limited | Financial services | 2021 |
| Manor Interior Solutions Limited | Construction | 2015 |
| Manor Walk Wellness Ltd | Other services | 2024 |
| Maple Property Bath Limited | Real estate | 2023 |
| Mapletec Ltd | Information & communication | 2015 |
| Marferg Ltd | Professional & scientific | 2020 |
| Marham Consulting Limited | Professional & scientific | 2023 |
| Mark Ferguson Limited | Administrative & support | 2012 |
| Mark Labudek Design Ltd | Professional & scientific | 2006 |
| Mark Smith Consulting Limited | Professional & scientific | 2019 |
| Mark Stenson Transport Ltd | Transport & logistics | 2014 |
| Market Harborough Building Society Charitable Foundation | Administrative & support | 1999 |
| Market Harborough Glazing Supplies Ltd | Construction | 2014 |
| Market Harborough Golf Club Limited | Arts & recreation | 2012 |
| Market Harborough Joinery Ltd | Construction | 2012 |
| Market Harborough Medical Services Limited | Health & social care | 2013 |
| Market Harborough Rufc Ltd | Arts & recreation | 2011 |
| Market Harborough Windows & Doors Ltd | Construction | 2026 |
| Market SH Limited | Hospitality | 2021 |
| Marquess Investment Holdings Ltd | Real estate | 2021 |
| Marquess Tax Ltd | Professional & scientific | 2020 |
| Marshall CGT LLP | | 2012 |
| Marshallco Ltd | Wholesale & retail | 2025 |
| Marston Steam & Vintage Restorations Limited | Professional & scientific | 2022 |
| Marston Steam & Vintage Show Limited | Administrative & support | 2022 |
| Martha Hill Limited | Professional & scientific | 1942 |
| Martins Arms Ltd | Hospitality | 2020 |
| Marton Engineering (Midlands) Limited | Other services | 2022 |
| Martyn Jones & Associates Limited | Professional & scientific | 1995 |
| Marv Percussion Ltd | Arts & recreation | 2025 |
| Maschinetek Limited | Manufacturing | 2018 |
| Masic Construction Ltd | Construction | 2018 |
| Masic Properties Limited | Real estate | 2026 |
| Massi Consultancy Ltd | Information & communication | 2018 |
| Master Accounting Limited | Professional & scientific | 2008 |
| Master Vehicle Sales Ltd | Wholesale & retail | 2015 |
| Matador Publishing Limited | Information & communication | 2013 |
| Matriz Consulting Limited | Professional & scientific | 2016 |
| Matt Dawson Motorsport Ltd | Transport & logistics | 2019 |
| MAX PI Ltd | Real estate | 2019 |
| Maxwell Barlow Lighting Limited | Professional & scientific | 2018 |
| Maxxi UK Limited | Manufacturing | 2013 |
| Mayfil Consortium Ltd | Wholesale & retail | 2016 |
| Maylan Commercial Properties Ltd | Real estate | 2011 |
| Maythorne Consultancy Ltd | Professional & scientific | 2024 |
| Maze Living Limited | Wholesale & retail | 2019 |
| Maze Rattan Limited | Wholesale & retail | 2009 |
| MB Performance Golf Ltd | Administrative & support | 2016 |
| Mbsb Properties (UK) Ltd | Real estate | 2017 |
| Mccready’S Home Improvements Ltd | Construction | 2025 |
| MCF Capital Ltd | Financial services | 2026 |
| Mcgarry-Gladstone Limited | Real estate | 2022 |
| Mcgrory Holdings Limited | Financial services | 2025 |
| Mclaughlin Recruitment Group UK Ltd | Administrative & support | 2023 |
| MCM Rail Consulting Ltd | Construction | 2015 |
| Mcneill Finance & Risk Solutions Ltd | Professional & scientific | 2009 |
| MCS Transport Ltd | Transport & logistics | 2015 |
| MDH Tackle Limited | Wholesale & retail | 2026 |
| MDT Consulting Limited | Professional & scientific | 2026 |
| Meadow View (Guilsborough) Developments Ltd | Construction | 2024 |
| Measham Road Investments Limited | Real estate | 2017 |
| Meat Link UK Limited | Manufacturing | 2001 |
| Medwell Hempson Farms Ltd T/A M H F Ltd | Agriculture & fishing | 1959 |
| Mega Yards Limited | Administrative & support | 2024 |
| MEM 1975 Limited | Wholesale & retail | 2024 |
| Membership Support Services Limited | Administrative & support | 2015 |
| Memre Song Ltd | Wholesale & retail | 2024 |
| Menaal Fast Food Ltd | Hospitality | 2025 |
| MENTOR2FREEDOM Ltd | Professional & scientific | 2023 |
| Merchant Contracts Ltd | Construction | 2019 |
| Meridia Management Services Limited | Wholesale & retail | 2013 |
| Merlinstone Property Ltd | Construction | 2026 |
| Merrall Consulting Ltd | Administrative & support | 2017 |
| Mexaport Limited | Extraterritorial | 2012 |
| MF Diesupplies Ltd | Manufacturing | 2023 |
| MGM Building & Property Maintenance Limited | Construction | 2010 |
| MGS Sporting LLP | | 2002 |
| MH PUB Ltd | Hospitality | 2025 |
| MH Rail Ltd | Construction | 2023 |
| MHT Foods Limited | Manufacturing | 2010 |
| Mhvw Estates Limited | Real estate | 1973 |
| Miavalentina Ltd | Wholesale & retail | 2019 |
| Michael Abbott Limited | Manufacturing | 2002 |
| Michael Gerard Consulting Ltd | Professional & scientific | 2002 |
| Michael Gerard Law Limited | Professional & scientific | 2018 |
| Michael Sheridan Creative Limited | Professional & scientific | 1994 |
| Mick Watts Plumbing & Heating Limited | Construction | 2019 |
| Micro Idea Limited | Professional & scientific | 2008 |
| Midas Cloud Communications Limited | Information & communication | 2020 |
| Midas Cloud Limited | Information & communication | 2026 |
| Midas Cloud Services Limited | Information & communication | 2026 |
| Midland Garden Rooms Ltd | Other services | 2017 |
| Midlands Car and Commercials Ltd | Wholesale & retail | 2017 |