| THE Vets Cardiff Limited | Professional & scientific | 2026 |
| THE Village Directory Limited | Professional & scientific | 2006 |
| THE Vowles Group Limited | Financial services | 2023 |
| THE Wandering Cosmos Ltd | Information & communication | 2022 |
| THE Welsh Association of Youth Clubs | Health & social care | 1991 |
| THE Will Consultancy Limited | Other services | 1990 |
| Thegreenrooms Ltd | Arts & recreation | 2018 |
| Thekitchenguy Ltd | Construction | 2019 |
| Thinkdif Limited | Health & social care | 2023 |
| Thinkdotsmart Ltd | Professional & scientific | 2024 |
| Thinkmed Ltd | Education | 2023 |
| Thinkteam Ltd | Administrative & support | 2025 |
| Thomas & SON Farm Ltd | Agriculture & fishing | 2025 |
| Thomas Vaughan Ltd | Wholesale & retail | 2008 |
| Thorne Property Sales Ltd | Real estate | 2023 |
| Three Kings Developments Ltd | Construction | 2026 |
| Thrivelifestylecafe Ltd | Hospitality | 2025 |
| THU Hoang Properties Ltd | Real estate | 2023 |
| Ti-Sha Services Ltd | Health & social care | 2022 |
| Tickets & Tours Ltd | Administrative & support | 2022 |
| Tidy Print and Promotional Limited | Manufacturing | 2018 |
| Tilly Investments Limited | Real estate | 2016 |
| Timoss Consultancy Ltd | Wholesale & retail | 2026 |
| Tinted Vision Commercial Ltd | Wholesale & retail | 2018 |
| Tinted Vision UK Ltd | Wholesale & retail | 2013 |
| Tiny Enterprises Limited | Wholesale & retail | 2013 |
| Tinytech Hub Ltd | Wholesale & retail | 2025 |
| Tipsy OWL CYF | Hospitality | 2022 |
| Tlcs Solutions Ltd | Construction | 2024 |
| TME Ventures Ltd | Real estate | 2024 |
| TN Pontypridd Nail Ltd | Other services | 2026 |
| Toetal Footcare Limited | Wholesale & retail | 2010 |
| Tollhurst Limited | Construction | 1990 |
| TOM Developments Ltd | Real estate | 2019 |
| TOM Norton Drylining & Ceilings Limited | Construction | 2016 |
| Tom's Garden Renovations Limited | Administrative & support | 2026 |
| Tomkinson Trading (South Wales) Ltd | Professional & scientific | 2025 |
| Tomsfx Ltd | Information & communication | 2019 |
| Tonna Stores Ltd | Wholesale & retail | 2026 |
| Tonteg Car Parking LOT Limited | Real estate | 2024 |
| Tonteg Stores Limited | Wholesale & retail | 2021 |
| Tool Hatch Limited | Wholesale & retail | 2024 |
| Top Notch Carpentry and Cabins Limited | Manufacturing | 2018 |
| Toprated Holding Limited | Wholesale & retail | 2023 |
| Torchwood Technologies Ltd | Other services | 2007 |
| Torfaen Maintenance Services Limited | Construction | 2014 |
| Total Envelope Repairs & Maintenance Ltd | Construction | 2026 |
| Total Facade Solutions Limited | Professional & scientific | 2009 |
| Total Fire Solutions (South) Holdings Limited | Financial services | 2022 |
| Total Fire Solutions (South) Limited | Construction | 2005 |
| Total Tanning Limited | Other services | 2018 |
| Totaltuning Limited | Wholesale & retail | 2010 |
| Town & Country Estates (London) Limited | Administrative & support | 1997 |
| TPG Group Holdings Ltd | Construction | 2015 |
| TPG Properties Ltd | Real estate | 2017 |
| Trackms Ltd | Manufacturing | 2020 |
| Trackside Engineering Ltd | Other services | 2017 |
| Tradesaleswales Limited | Wholesale & retail | 2016 |
| Trailcraft MTB and BMX Track Construction Ltd | Construction | 2013 |
| Train Your Pulse Ltd | Information & communication | 2019 |
| Transport for Wales | Professional & scientific | 2015 |
| Transport for Wales Rail Ltd | Transport & logistics | 2020 |
| Treble Media Ltd | Information & communication | 2020 |
| Treehouse Management Ltd | Extraterritorial | 2014 |
| Treforest Delight Limited | Hospitality | 2024 |
| Treforest Service Centre Ltd | Wholesale & retail | 2021 |
| Treforest Veterinary Clinic Limited | Professional & scientific | 2011 |
| Treforest Windows and Glass Solutions Ltd | Manufacturing | 2020 |
| Trentkey Limited | Transport & logistics | 1991 |
| Treorchy Pharmacy Limited | Wholesale & retail | 2019 |
| TREVOR151068 Limited | Extraterritorial | 2013 |
| TRI Seren Property Ltd | Real estate | 2026 |
| Tricwm Limited | Construction | 2025 |
| Trillions Media Ltd | Wholesale & retail | 2026 |
| Trilloe’S Ltd | Construction | 2026 |
| Trldeliveries Ltd | Wholesale & retail | 2024 |
| Troed-Y-Rhiw Horse Training Limited | Agriculture & fishing | 2021 |
| Trojan Construction (UK) Employee Ownership Trustee Limited | Professional & scientific | 2023 |
| Trojan Construction (UK) Limited | Professional & scientific | 2013 |
| Trojan Construction Management Limited | Construction | 2012 |
| Trojan Estates (UK) Limited | Real estate | 2013 |
| Trust Vision Limited | Extraterritorial | 2013 |
| Trusted Herc Auto Co., Ltd | Wholesale & retail | 2025 |
| Trustytravelpontypridd Limited | Transport & logistics | 2026 |
| Tscc Computing Limited | Information & communication | 2012 |
| Tugbury Group Ltd | Financial services | 2020 |
| Tugbury Security Ltd | Administrative & support | 2019 |
| Tumama Kids Care (UK) Company Limited | Wholesale & retail | 2024 |
| Tunnel Engineering Solutions Limited | Mining & quarrying | 2021 |
| Turone (LB) Ltd | Administrative & support | 2026 |
| Turone (LS) Ltd | Professional & scientific | 2024 |
| Turone Ltd | Professional & scientific | 2022 |
| TV & Film Security Services Ltd | Administrative & support | 2025 |
| Tw&T Limited | Construction | 2025 |
| Twenty D Ltd | Transport & logistics | 2018 |
| TWF Consultant Limited | Information & communication | 2023 |
| TWI Creator Network Ltd | Information & communication | 2026 |
| TWO4 Martial Arts Ltd | Arts & recreation | 2020 |
| TWT LOL CYF | Manufacturing | 2014 |
| TY Bryn Gardens Management Company Limited | Households | 2010 |