| MT Lift Services Ltd | Manufacturing | 2024 |
| MTA Pharmacy Services Ltd | Health & social care | 2022 |
| MTD Made Easy Ltd | Professional & scientific | 2024 |
| Mtech UK Holdings Ltd | Manufacturing | 2013 |
| Mtoma Ltd | Manufacturing | 2025 |
| MTW Direct Limited | Wholesale & retail | 2007 |
| MTW Engineering (Swansea) Limited | Wholesale & retail | 2025 |
| MU-90-LOGISTICS Ltd | Transport & logistics | 2026 |
| Mucky Mutz Ltd | Other services | 2021 |
| MUD Landscape Ltd | Professional & scientific | 2025 |
| Mufans Healthcare Limited | Wholesale & retail | 2023 |
| Mugba Ltd | Wholesale & retail | 2018 |
| Muggz Limited | Wholesale & retail | 2019 |
| Mullen Engineering Limited | Professional & scientific | 2019 |
| Multiserve FM Ltd | Administrative & support | 2025 |
| Multitrade Property Care Ltd | Construction | 2018 |
| Mumbai (Swansea) Limited | Hospitality | 2022 |
| Mumbales Houses Ltd | Real estate | 2022 |
| Mumbales Limited | Wholesale & retail | 2021 |
| Mumbles Brewery Ltd | Manufacturing | 2011 |
| Mumbles Brewery TAP Room Limited | Hospitality | 2024 |
| Mumbles Brewing Company Limited | Manufacturing | 2014 |
| Mumbles Coffee Limited | Wholesale & retail | 2013 |
| Mumbles Cricket Club Limited | Arts & recreation | 2019 |
| Mumbles Cutting Crew Limited | Other services | 2011 |
| Mumbles Development Trust Limited | Other services | 1999 |
| Mumbles Drycleaning and Laundry Limited | Other services | 2015 |
| Mumbles DS Ltd | Health & social care | 2018 |
| Mumbles Electric Gates Ltd | Construction | 2026 |
| Mumbles Fine Wines Limited | Wholesale & retail | 1980 |
| Mumbles Flooring Ltd | Wholesale & retail | 2010 |
| Mumbles GAS Services Ltd | Construction | 2015 |
| Mumbles GIN & Tapas Ltd | Hospitality | 2023 |
| Mumbles Hospitality Limited | Hospitality | 2022 |
| Mumbles Housing Limited | Real estate | 2017 |
| Mumbles Imaging Limited | Health & social care | 2016 |
| Mumbles Kitchen Studio Ltd | Wholesale & retail | 2013 |
| Mumbles Methodist Open Door Company Limited | Hospitality | 2004 |
| Mumbles Place Limited | Hospitality | 2026 |
| Mumbles Podiatry Ltd | Health & social care | 2015 |
| Mumbles Property Consultants Limited | Construction | 2018 |
| Mumbles Property Limited | Construction | 2019 |
| Mumbles Reach Management Company Limited | Households | 2013 |
| Mumbles RFC 2024 Limited | Arts & recreation | 2024 |
| Mumbles Road Limited | Hospitality | 2020 |
| Mumbles Rugby Football Club Limited | Arts & recreation | 2018 |
| Mumbles.Life Ltd | Information & communication | 2026 |
| Muna REB Ltd | Wholesale & retail | 2026 |
| Munch Machine Limited | Hospitality | 2024 |
| Munchies Hafod Ltd | Hospitality | 2024 |
| Munesu Limited | Professional & scientific | 2024 |
| Murton Farm Ltd | Agriculture & fishing | 2019 |
| Musa Property Management Limited | Real estate | 2025 |
| Muse Care Ltd | Information & communication | 2018 |
| Mushroom Properties Ltd | Real estate | 2025 |
| Music UN Limited | Extraterritorial | 2013 |
| Musicality Choir Ltd | Information & communication | 2026 |
| Muslim Chaplaincy and Spiritual Care Limited | Professional & scientific | 2026 |
| Muswanna Limited | Hospitality | 2021 |
| Muton Limited | Information & communication | 2007 |
| Mutt Struts (Swansea) Ltd | Other services | 2019 |
| Mutual Expansion Trust Limited | Administrative & support | 1939 |
| Muz's Enterprise Limited | Wholesale & retail | 2017 |
| MV V-Fit Limited | Other services | 2025 |
| MV Voltmasters Ltd | Construction | 2025 |
| Mvsh Limited | Health & social care | 2023 |
| Mvsl Design and Print Ltd | Manufacturing | 2021 |
| Mvst Properties Limited | Real estate | 2021 |
| Mvstretail Limited | Wholesale & retail | 2025 |
| MW Consult Ltd | Professional & scientific | 2018 |
| MW Properties NO 66 Limited | Professional & scientific | 2007 |
| MW1 Dental Limited | Health & social care | 2019 |
| Mwnki Ltd | Professional & scientific | 2012 |
| Mwsoffshorerep Limited | Professional & scientific | 2014 |
| Mwtch Ltd | Hospitality | 2024 |
| My Beard Battle Ltd | Wholesale & retail | 2024 |
| My Digs Ltd | Real estate | 2019 |
| My Energy Switch Ltd | Administrative & support | 2014 |
| My Gene Trait Ltd | Health & social care | 2019 |
| My Heart in Mind Ltd | Health & social care | 2023 |
| My Holiday Taxi Ltd | Transport & logistics | 2023 |
| My Mega Media Ltd | Extraterritorial | 2023 |
| My Professional Dreams Sports Management Limited | Arts & recreation | 2016 |
| My Recruitment Hub Ltd | Administrative & support | 2021 |
| My ROB Limited | Administrative & support | 2023 |
| My Swim Co. Limited | Arts & recreation | 2026 |
| My Time IS Very Limited | Extraterritorial | 2012 |
| Myedpsych Ltd | Health & social care | 2021 |
| Mygeneration Limited | Administrative & support | 2014 |
| Myherd Ltd | Information & communication | 2025 |
| Mylesjenkins Electrical Limited | Construction | 2023 |
| Myllex Limited | Administrative & support | 2018 |
| Mylo Invest Ltd | Professional & scientific | 2017 |
| Mylos Coffee Limited | Hospitality | 2026 |
| Myls Food and Wine Ltd | Wholesale & retail | 2026 |
| Mynydd Limited | Administrative & support | 2010 |
| Mynydd Lliw Common Land Limited | Agriculture & fishing | 2000 |
| Mystical Sea Limited | Arts & recreation | 2016 |
| Mythicmew Limited | Wholesale & retail | 2025 |
| Myty Homes Limited | Households | 2016 |