| Transpass Ltd | Transport & logistics | 2021 |
| Transport Newport Limited | Transport & logistics | 2025 |
| Transport South West Ltd | Transport & logistics | 2026 |
| Transport-Able Logistics Ltd | Wholesale & retail | 2022 |
| Traston Holdings Limited | Real estate | 1982 |
| Traston Welders Limited | Manufacturing | 1990 |
| Trauma Simulation Limited | Professional & scientific | 2013 |
| Travel & Tourism Worldwide Ltd | Administrative & support | 2024 |
| Travel Ease Consultants Limited | Administrative & support | 2025 |
| Travsky Ltd | Extraterritorial | 2024 |
| Tray's Trackers Limited | Wholesale & retail | 2019 |
| Treasure Point Ltd | Wholesale & retail | 2025 |
| Treatment Room Physio Limited | Other services | 2018 |
| Treats&Eats Bakeshop Limited | Hospitality | 2025 |
| Trecelyn Chiefs Ltd | Manufacturing | 2025 |
| Tred Films Limited | Information & communication | 2019 |
| Tredegar Park Golf Club Limited | Arts & recreation | 1940 |
| Tredomen Ltd | Construction | 2015 |
| Tree Finesse Forestry Machinery Limited | Agriculture & fishing | 2016 |
| Tregare Farms Limited | Agriculture & fishing | 2011 |
| Treharne Solutions Limited | Professional & scientific | 2024 |
| Trend Globe Ltd | Wholesale & retail | 2025 |
| Trendz Hair Ltd | Other services | 2024 |
| Trent Mews Management Company Limited | Real estate | 2006 |
| Trentham Wings Co Limited | Hospitality | 2025 |
| Treowen Wind Consultancy Ltd | Construction | 2025 |
| Tretower Ltd | Professional & scientific | 2015 |
| Trew Carpentry Limited | Manufacturing | 2023 |
| Tri-Aqua Cleaning Limited | Administrative & support | 2008 |
| Triad Holdings Ltd | Extraterritorial | 2009 |
| Triangle Clothing Limited | Wholesale & retail | 2025 |
| Triangle HR Limited | Professional & scientific | 2008 |
| Trichem Wales Limited | Wholesale & retail | 1996 |
| Tricloud Limited | Households | 1981 |
| Trigg Locums Ltd | Health & social care | 2015 |
| Trigwell Cosmetics Limited | Wholesale & retail | 2026 |
| Trigwell Investments Limited | Real estate | 2023 |
| Trike Shop (UK) Limited | Wholesale & retail | 2002 |
| Trimarine Advanced Marine Projects Ltd. | Professional & scientific | 1995 |
| Trimini Properties Ltd | Real estate | 2024 |
| Trinant Stores Limited | Wholesale & retail | 2021 |
| Trinidad Investments Limited | Real estate | 2016 |
| Trinity Court Management Company (Ryde) Limited | Households | 1987 |
| Trinity Court Newport Limited | Professional & scientific | 2015 |
| Trinity Design & Build (Wales) Ltd | Construction | 2014 |
| Trinity Flooring Limited | Construction | 2026 |
| Trinity Residential Management Company Limited | Households | 2022 |
| Trinity Road Management (Ventnor) Company Limited | Households | 2021 |
| Trinty FM (UK) Ltd | Construction | 2020 |
| Trio Business Consultants LLP | | 2017 |
| Tripdatabase Limited | Information & communication | 2001 |
| Triplefax Limited | Hospitality | 2025 |
| Triplesnap Technologies Ltd | Information & communication | 2023 |
| Triumph Park Ltd | Real estate | 2022 |
| Tropaquatics Ltd | Agriculture & fishing | 2026 |
| Trouville Investments LLP | | 2018 |
| Trows Estates Limited | Real estate | 2025 |
| TRS Fleet Management Limited | Wholesale & retail | 2014 |
| TRS Global Ltd | Financial services | 2024 |
| Truck Mounted Forklifts (Wales) Limited | Manufacturing | 2015 |
| Truck Support Ltd | Wholesale & retail | 2018 |
| Truckeco Logistics Ltd | Transport & logistics | 2026 |
| True Journeys Healthcare Ltd | Health & social care | 2025 |
| True Story Celebrant Ltd | Professional & scientific | 2025 |
| True Volt Electrical Ltd | Construction | 2024 |
| Trueline Treatments Limited | Professional & scientific | 2007 |
| Truelume Films Ltd | Information & communication | 2025 |
| Truestyle Limited | Wholesale & retail | 2011 |
| Trufold Ltd. | Manufacturing | 2013 |
| Trulife Financial Ltd | Financial services | 2020 |
| Trura Limited | Other services | 2022 |
| Truscott Capital Ltd | Financial services | 2024 |
| Trust Drive Ltd | Wholesale & retail | 2025 |
| Trust Productions Ltd | Information & communication | 2017 |
| Trusted Designs Limited | Extraterritorial | 2021 |
| Trusted Homecare Ltd | Health & social care | 2023 |
| Trusted Xperts Limited | Information & communication | 2013 |
| Trusty Holdings Ltd | Wholesale & retail | 2025 |
| Truthasis Ltd | Wholesale & retail | 2025 |
| Trychywmad Property Ltd | Real estate | 2017 |
| Trydn Bikes Ltd | Wholesale & retail | 2025 |
| Tsdelivery Limited | Transport & logistics | 2025 |
| Tshampers Ltd | Wholesale & retail | 2025 |
| TSK Management Accounting Services Ltd | Professional & scientific | 2015 |
| Tspn Express Ltd | Hospitality | 2021 |
| Ttan Limited | Health & social care | 2018 |
| TTB Brickwork Ltd | Construction | 2024 |
| Ttml UK Ltd | Transport & logistics | 2025 |
| TTT Hospitality Limited | Hospitality | 2026 |
| Tube and Steel Supplies Ltd. | Wholesale & retail | 1999 |
| Tuche Ltd | Administrative & support | 2011 |
| Tucker @ Sons Building Contractors Ltd | Construction | 2018 |
| Tudor-Jones Sourcing and Consulting Limited | Wholesale & retail | 2023 |
| Tudosa Valentin Limited | Other services | 2015 |
| Tuendi 01 Ltd | Administrative & support | 2024 |
| Tuendi Capital Ltd | Administrative & support | 2023 |
| Tuffrey Consulting Ltd | Professional & scientific | 2010 |
| Tuksy Autocentre Ltd | Wholesale & retail | 2024 |
| Tuksy Chauffeurs Cardiff Limited | Transport & logistics | 2019 |
| Tuksy Chauffeurs Ltd | Transport & logistics | 2014 |