| THE 3G'S Development Trust | Information & communication | 1999 |
| THE Bait Shack (Merthyr) Ltd | Wholesale & retail | 2025 |
| THE Bessemer Hotel Carvery & Grill Ltd | Hospitality | 2018 |
| THE Bevan Foundation | Education | 2001 |
| THE Big Heart of Merthyr Tydfil | Other services | 2012 |
| THE Black Pitcher Roastery Ltd | Manufacturing | 2026 |
| THE Cake and Sugarcraft Store Limited | Manufacturing | 2015 |
| THE Carbon Economy College CYF | Hospitality | 2020 |
| THE Carpet & BED Co (Merthyr) Limited | Wholesale & retail | 2011 |
| THE Cheesecake GUY Ltd | Wholesale & retail | 2020 |
| THE Coach House Holdings Group Limited | Real estate | 2026 |
| THE Colour House Signs Limited | Administrative & support | 2025 |
| THE Contracting Group Ltd | Construction | 2019 |
| THE Cyfarthfa Foundation | Education | 2020 |
| THE Enfield Printing Company Limited | Manufacturing | 1977 |
| THE Fire Practice Ltd | Professional & scientific | 2014 |
| THE Fitness Locker Ltd | Arts & recreation | 2015 |
| THE Green House Well Limited | Wholesale & retail | 2019 |
| THE Guest Keen Ltd | Hospitality | 2015 |
| THE Handwork Finishing Company LLP | | 2010 |
| THE Lighthouse Campaign CIC | Health & social care | 2025 |
| THE Loop Online Limited | Professional & scientific | 2007 |
| THE Magazine Printing Company Limited | Extraterritorial | 2018 |
| THE Merthyr Tydfil and District Naturalists' Society | Other services | 2002 |
| THE Merthyr Tydfil Institute for the Blind | Manufacturing | 1991 |
| THE New Crown (Merthyr Tydfil) Limited | Hospitality | 2016 |
| THE New W1NDS0R Bar Ltd | Hospitality | 2023 |
| THE Next Elite Services Ltd | Information & communication | 2025 |
| THE NYE Family Assessment Resource Limited | Public administration | 2021 |
| THE Pant & Dowlais Boys & Girls Club | Arts & recreation | 2011 |
| THE Pant & Dowlais Community Engine House | Arts & recreation | 2008 |
| THE Personal Training Room Limited | Arts & recreation | 2024 |
| THE Physique Academy Coaching Ltd | Education | 2025 |
| THE Roost Merthyr Tydfil Ltd | Hospitality | 2017 |
| THE Silver Bullet PUB Limited | Hospitality | 2012 |
| THE Strangling Fruit Ltd | Professional & scientific | 2022 |
| THE Swim Labs - Merthyr Ltd | Arts & recreation | 2026 |
| THE Takeout Merthyr Limited | Hospitality | 2024 |
| THE Tenneco Automotive (UK) Pension Scheme Trustee Limited | Administrative & support | 2000 |
| THE Tuck in Merthyr Limited | Hospitality | 2018 |
| THE Vapor DEN Brecon Limited | Wholesale & retail | 2015 |
| THE View Camping Ltd | Hospitality | 2019 |
| THE Wellness Centre Merthyr CIC | Health & social care | 2024 |
| THE White Horse Merthyr Tydfil Ltd | Hospitality | 2024 |
| Theflames Ltd | Hospitality | 2026 |
| Themunchstop Ltd | Hospitality | 2026 |
| Theomnivorous Ltd | Hospitality | 2025 |
| Thermocooling Services Limited | Manufacturing | 2009 |
| Thisha Private Limited | Wholesale & retail | 2024 |
| Thomas & Davies (Merthyr Tydfil) Limited | Wholesale & retail | 1962 |
| Three Knights Property Group Ltd | Real estate | 2025 |
| Three TCS Merthyr LLP | | 2013 |
| Tidy Burger Ltd | Hospitality | 2025 |
| Tier 1 Construction Services Ltd | Construction | 2019 |
| Tier 1 Property Limited | Real estate | 2021 |
| Tilltom Property Developments Ltd | Construction | 2025 |
| Timberline Construction Ltd | Construction | 2023 |
| Timtom Studio Limited | Information & communication | 2026 |
| Tjpi Ltd | Transport & logistics | 2025 |
| TK Tattoo Kingdom Ltd | Other services | 2020 |
| TKJ Properties Limited | Real estate | 2017 |
| TM Properties (South Wales) Ltd | Real estate | 2020 |
| Toast & Timber Ltd | Hospitality | 2026 |
| TOM Bedford Media Ltd | Information & communication | 2015 |
| Tommie’S Timbers Ltd | Construction | 2023 |
| Tommy's Bar Limited | Construction | 2024 |
| Top Barber Style Ltd | Other services | 2025 |
| Top Indian Food Ltd | Hospitality | 2024 |
| Top Table Catering Hire Limited | Hospitality | 2006 |
| Toplinecreative Limited | Manufacturing | 2020 |
| Torbay Caravans Ltd | Hospitality | 2009 |
| Total Staffing Solutions Employee Ownership Trustee Ltd | Professional & scientific | 2023 |
| Total Staffing Solutions Ltd | Administrative & support | 2016 |
| Touch Voice and Data Limited | Information & communication | 2012 |
| Tour Vans Ltd | Administrative & support | 2025 |
| TPM Properties Ltd | Real estate | 2019 |
| TPT Consultancy & Training Limited | Administrative & support | 2014 |
| Trace Developments Limited | Construction | 2024 |
| Tracey's Transport Limited | Transport & logistics | 2026 |
| Trackway Ltd | Transport & logistics | 2025 |
| Tramping Transport Ltd | Transport & logistics | 2025 |
| TRD1 Property Ltd | Real estate | 2022 |
| Treasured Embrace Ltd | Manufacturing | 2024 |
| Trecatti (Dowlais) Charitable Trust | Administrative & support | 2007 |
| Treharris Boys and Girls Club | Other services | 2009 |
| Tribotics Limited | Professional & scientific | 2003 |
| Trilithon Ltd | Professional & scientific | 2025 |
| Trinity Childcare and Family Centre Ltd. | Education | 2012 |
| Triple Apple Limited | Hospitality | 2020 |
| TRM Sullivan Ltd | Wholesale & retail | 2018 |
| Troedyrhiw Commercial Ltd | Real estate | 2022 |
| Troedyrhiw Garage Limited | Wholesale & retail | 2024 |
| Troy Williams Trading Ltd | Hospitality | 2020 |
| Truluck Engineering Limited | Professional & scientific | 2012 |
| Trydan Events Ltd | Arts & recreation | 2022 |
| Trydan Property Ltd | Real estate | 2019 |
| TW Property Surveys Limited | Information & communication | 2017 |
| Two Wheel Salvage Ltd | Wholesale & retail | 2025 |
| Twyn Fish Bar Limited | Hospitality | 2025 |
| TY Thai Ltd | Hospitality | 2026 |