| Literature Stitches Limited | Wholesale & retail | 2025 |
| Little Messy's Limited | Arts & recreation | 2012 |
| Little Nanny's Limited | Wholesale & retail | 2020 |
| Liveacts Ltd | Professional & scientific | 2025 |
| LJ Roofers Ltd | Construction | 2025 |
| LJH Care Services Limited | Health & social care | 2021 |
| Ljswind Ltd | Construction | 2025 |
| LK Property and Landscaping Services Ltd | Construction | 2021 |
| LK Property Group Ltd | Real estate | 2021 |
| Llay Properties Limited | Real estate | 2018 |
| LMC Car Buying Services Limited | Wholesale & retail | 2020 |
| LMH Catering Ltd | Hospitality | 2026 |
| Locial Limited | Information & communication | 2020 |
| Lotus Cladding Solutions Ltd | Construction | 2022 |
| Louise & Claire's Services Ltd | Health & social care | 2015 |
| LOW Bridge Business Park Limited | Administrative & support | 2008 |
| LT Nails Ltd | Other services | 2024 |
| Lucida Construction Limited | Construction | 2016 |
| Lucky Buddha Media Limited | Other services | 2018 |
| Lucky Star 2876 Ltd | Hospitality | 2025 |
| Lucky Zheng Limited | Hospitality | 2019 |
| Luluz Limited | Hospitality | 2023 |
| Luxstuff Ltd | Wholesale & retail | 2026 |
| Luxury SB Ltd | Manufacturing | 2022 |
| M & J Engineering Services Ltd | Professional & scientific | 2003 |
| M & S Taylor Properties Limited | Real estate | 2020 |
| M a Moffatt Transport Ltd | Transport & logistics | 2013 |
| M K J Joinery Ltd | Construction | 2021 |
| M&S Taylor Maintenance Ltd | Construction | 2021 |
| M'S Barber Style Ltd | Other services | 2025 |
| M. Farren Limited | Wholesale & retail | 1983 |
| M. Pippard Ltd | Wholesale & retail | 2003 |
| M.A.C. Event Planning Limited | Other services | 2025 |
| M.A.C. Metalcraft Ltd | Other services | 1987 |
| M.E. Schofield Properties Limited | Real estate | 2023 |
| M18 TVP Ltd | Real estate | 2026 |
| M4BITES Ltd | Wholesale & retail | 2025 |
| M900 Ltd | Transport & logistics | 2024 |
| Macelands Limited | Real estate | 2004 |
| Mactech Systems Limited | Manufacturing | 2001 |
| Maggies Construction Limited | Construction | 2024 |
| Mainstall Ltd | Construction | 2025 |
| Maison Vertes Limited | Financial services | 2018 |
| Majeed & Abdul Ltd | Hospitality | 2025 |
| Majeed & Anas Ltd | Hospitality | 2025 |
| Majiclad Ltd | Construction | 2025 |
| Mala Logistics Limited | Transport & logistics | 2025 |
| Mallorca Bike Hire Limited | Wholesale & retail | 2017 |
| MAN Industrial Supplies Limited | Administrative & support | 2000 |
| Man's Hungry Ltd | Hospitality | 2025 |
| Mane Metering Holdings Limited | Financial services | 2019 |
| Mangham EC and I Solutions Ltd | Professional & scientific | 2024 |
| Manor Garage (Mexborough) Limited | Wholesale & retail | 2003 |
| MAR Energy Solutions Ltd | Other services | 2019 |
| Marchman (2001) Limited | Real estate | 2001 |
| Maredan Limited | Professional & scientific | 2025 |
| Marglo Ltd | Wholesale & retail | 2014 |
| Mark Baines Motorsport Limited | Professional & scientific | 2020 |
| Mark Epton Ltd | Construction | 2018 |
| Mark Rollinson Builders Limited | Construction | 2007 |
| Mark Wilds Financial Services Ltd | Financial services | 2011 |
| Markham Enterprises Limited | Health & social care | 2014 |
| Marley Court Care Home Limited | Health & social care | 2021 |
| Matt Hague Consulting Limited | Wholesale & retail | 2023 |
| MC Sportswear Ltd | Wholesale & retail | 2024 |
| Mcgivern Reporting Services Ltd | Health & social care | 2019 |
| Mclaughlin Productions Ltd | Administrative & support | 2026 |
| MDB Accountancy Services Ltd | Professional & scientific | 2025 |
| MDH Cleaning Ltd | Administrative & support | 2022 |
| MDJ Mechanical Designs Limited | Professional & scientific | 2022 |
| Meadow Interiors Limited | Wholesale & retail | 2016 |
| MED Beds Limited | Construction | 2005 |
| Medlock & Sons Limited | Construction | 2006 |
| Medusa Multi Feeding Systems Limited | Manufacturing | 2001 |
| MEG Scaffolding Ltd | Construction | 2024 |
| Memcare Ltd | Information & communication | 2020 |
| Mennelli Ropeworks Limited | Construction | 2016 |
| Menopause Expert Limited | Health & social care | 2022 |
| Meoc Training Limited | Administrative & support | 2004 |
| Merlin Metal Recycling Ltd | Manufacturing | 2023 |
| Merlin Properties (Sheffield) Ltd | Real estate | 2019 |
| Metalian Ltd | Water & waste | 2024 |
| MEX Borough OFF Licence Ltd | Wholesale & retail | 2020 |
| MEX News Market Ltd | Wholesale & retail | 2025 |
| Mexborough & District Heritage Society Limited | Arts & recreation | 2025 |
| Mexborough Athletic Social Club Limited | Hospitality | 2003 |
| Mexborough Business Centre Limited | Real estate | 2015 |
| Mexborough Car Testing Centre Limited | Wholesale & retail | 2011 |
| Mexborough Christian Community Centre Limited | Other services | 2019 |
| Mexborough Mini Market Ltd | Wholesale & retail | 2013 |
| Mexborough Mobility Limited | Wholesale & retail | 2016 |
| Mexborough Store IT Ltd | Wholesale & retail | 2019 |
| Mexbro Fisheries Limited | Hospitality | 2026 |
| Mexbrough Mini Market Ltd | Wholesale & retail | 2024 |
| Mexden Limited | Health & social care | 2026 |
| Mezza Pizza Ltd | Hospitality | 2026 |
| MGR Editorial Ltd | Information & communication | 2019 |
| MIA Waste OIL Ltd | Water & waste | 2018 |
| Michael Coward Limited | Financial services | 2025 |
| Michael Torr Developments Limited | Wholesale & retail | 2015 |