| Marklan Company Ltd | Wholesale & retail | 2024 |
| Marks Away Limited | Construction | 2012 |
| Marks Trade Cars Ltd | Wholesale & retail | 2020 |
| Marlz Ltd | Wholesale & retail | 2025 |
| Marmaris Grill Ltd | Hospitality | 2025 |
| Marmaville Court RTM Company Limited | Households | 2017 |
| Mars Investments Ltd | Real estate | 2024 |
| Mars Webb PR Limited | Professional & scientific | 2017 |
| Marsh Street Motors Limited | Wholesale & retail | 2020 |
| Marshall (Wath) Limited | Real estate | 1996 |
| Marshall Brothers Developments Limited | Construction | 2019 |
| Marshall Brothers Ltd | Manufacturing | 2017 |
| Marshall Cleaning Services Ltd | Administrative & support | 2018 |
| Marsham Street Properties Limited | Real estate | 2009 |
| Marske Country Estate Ltd | Real estate | 2026 |
| Martial Machinations Ltd | Other services | 2018 |
| Martin Lowe (Automatic Transmissions) Limited | Wholesale & retail | 1988 |
| Marvelora Ltd | Health & social care | 2026 |
| Marviik Ltd | Manufacturing | 2025 |
| Marwa.D Ltd | Construction | 2021 |
| Mary John Limited | Health & social care | 2025 |
| Mary Street Little Houghton Ltd | Households | 2024 |
| Mascot Powder Coating and Blasting Limited | Manufacturing | 2026 |
| Mashkloset Ltd | Wholesale & retail | 2018 |
| Mason Building Contractors Limited | Construction | 2003 |
| Mason Building Homes Limited | Real estate | 2008 |
| Mason Companies Limited | Professional & scientific | 2008 |
| Mason Richards Marketing Ltd | Professional & scientific | 2010 |
| Mass Manka Courier Services Ltd | Transport & logistics | 2021 |
| Massarella Fisheries Ltd | Arts & recreation | 2022 |
| Master CUT (Barnsley) Ltd | Other services | 2024 |
| Master Mind Music Ltd | Information & communication | 2018 |
| Masterprint (Barnsley) Limited | Construction | 2020 |
| MAT Staff Ltd | Administrative & support | 2024 |
| Match Planners Limited | Information & communication | 2018 |
| Matei Logistics Limited | Transport & logistics | 2018 |
| Mateusz Czerwinski Limited | Transport & logistics | 2024 |
| Matfield Haulage Ltd | Transport & logistics | 2014 |
| Maths Tuition Online Limited | Education | 2021 |
| Matlock Wholesale Ltd | Wholesale & retail | 2025 |
| Matrix (Midlands) Limited | Construction | 2004 |
| Matrix Advanced Surveying Ltd | Professional & scientific | 2024 |
| Matrix Consulting Engineers Limited | Professional & scientific | 2016 |
| Matrix Installations Limited | Construction | 2015 |
| Matrix Property Development Ltd | Construction | 2024 |
| Matrix Rental Properties Limited | Hospitality | 2020 |
| Matt Appleby Yoga Limited | Education | 2021 |
| Mattbar Ltd | Professional & scientific | 2015 |
| Matteo Servtrans Ltd | Construction | 2019 |
| Matthew James Homes Yorkshire Ltd | Real estate | 2024 |
| Matthew Pover Ltd | Professional & scientific | 2012 |
| Mavril Limited | Wholesale & retail | 2017 |
| MAW Town Planning Ltd | Professional & scientific | 2019 |
| MAX Ellis Holdings Ltd | Administrative & support | 2023 |
| MAX Ellis Property Ltd | Real estate | 2020 |
| MAX Energy Consultancy Limited | Other services | 2021 |
| MAX MD Construct Ltd | Construction | 2019 |
| Maycheck Limited | | 1985 |
| Mayer Productions Ltd | Arts & recreation | 2004 |
| Mayes Property Services and Development Ltd | Construction | 2021 |
| Mayfield Barnsley Limited | Real estate | 2006 |
| Mayflower Gardens Management Company Limited | Households | 2006 |
| Mayflower Manor Ltd | Construction | 2015 |
| Maygold Limited | Households | 1987 |
| Mayson Investments Ltd | Financial services | 2022 |
| Mayson Security Services Limited | Administrative & support | 2004 |
| Maywood Containment Services Ltd | Professional & scientific | 2026 |
| Maywood Homes Yorkshire Ltd | Construction | 2021 |
| Mazhandu Limited | Manufacturing | 2024 |
| Mazon Group Ltd | Administrative & support | 2026 |
| MB Home Fragrance Ltd | Manufacturing | 2026 |
| MB Plumbing & Heating (Yorkshire) Limited | Construction | 2015 |
| MBA Businessense Ltd | Professional & scientific | 2003 |
| Mbaltic Brickwork Ltd | Construction | 2018 |
| MBC Business Improvement Solutions Limited | Professional & scientific | 2018 |
| MBH Transport Company Ltd | Transport & logistics | 2025 |
| MBI Couriers Ltd | Transport & logistics | 2023 |
| Mbooth Design Ltd | Professional & scientific | 2011 |
| MC Physiotherapy Limited | Health & social care | 2017 |
| MC Seveney Plumbing & Heating Services Limited | Construction | 2011 |
| MC Vape Supplies Limited | Wholesale & retail | 2022 |
| MC25 Management Ltd | Real estate | 2025 |
| Mcardle Business Management Ltd | Professional & scientific | 2025 |
| Mcaulay & Sons Limited | Manufacturing | 2024 |
| Mcbb Homes Ltd | Real estate | 2022 |
| Mccallum Manufacturing Limited | Manufacturing | 1987 |
| MCD Home & Garden (UK) Ltd. | Wholesale & retail | 2015 |
| Mcdev Healthcare Ltd | Health & social care | 2018 |
| MCG Legal Consultancy Services Ltd | Professional & scientific | 2020 |
| Mckay Commercial Interiors Limited | Construction | 2016 |
| Mckay Healthcare Ltd | Wholesale & retail | 2011 |
| Mckay Real Estate Ltd | Real estate | 2026 |
| Mckeefery Property Management Ltd | Real estate | 2022 |
| Mclean Group Holdings Limited | Financial services | 2024 |
| Mclean L Limited | Wholesale & retail | 2019 |
| Mcleod GUY Consulting Limited | Professional & scientific | 2014 |
| Mcqueens Textiles Limited | Wholesale & retail | 2002 |
| Mcquillans Family Butchers Limited | Wholesale & retail | 2003 |
| MCR Stage Ltd | Hospitality | 2025 |
| Mcrc Properties Limited | Real estate | 2023 |