| Tommy Tubs Ltd | Arts & recreation | 2022 |
| Toner Construction Contracts Ltd | Construction | 2023 |
| Toner Enterprises Ireland Ltd | Hospitality | 2017 |
| Toner Property Management Ltd | Real estate | 2025 |
| Tony Havern Joinery Ltd | Construction | 2014 |
| Tony Mcaleavey Group Ltd | Real estate | 2021 |
| Top Deal Mobiles Ltd | Wholesale & retail | 2023 |
| Top House Kitchens Limited | Manufacturing | 2021 |
| Top Marques Trading Ltd | Wholesale & retail | 2021 |
| Top Oils Newry Ltd | Wholesale & retail | 2016 |
| Top Rank Imports Ltd | Wholesale & retail | 2025 |
| Top Truck Exports Ltd | Wholesale & retail | 2023 |
| Topdog Prizes Ltd | Arts & recreation | 2025 |
| Topex Merchants L.P. | | 2017 |
| Topflight Holidays Limited | Administrative & support | 1991 |
| Topney Equine Limited | Agriculture & fishing | 2016 |
| Torrbeg Properties Limited | Real estate | 2019 |
| Total Electrical Inspection and Testing Limited | Construction | 2007 |
| Townview Hire Limited | Administrative & support | 2023 |
| Toyztore Limited | Extraterritorial | 2004 |
| Tpbb Property Management Ltd | Real estate | 2018 |
| TPS Caravan Park Ltd | Hospitality | 2023 |
| TPT Auctions Ltd | Wholesale & retail | 2022 |
| TQ Contracts Ltd | Construction | 2018 |
| Traclink Ltd | Manufacturing | 2022 |
| Tracy Tookey Consulting Limited | Professional & scientific | 2023 |
| Trade Made Limited | Manufacturing | 2023 |
| Tradecraft Building Products (NI) Limited | Wholesale & retail | 2016 |
| Tradesmith Trans L.P. | | 2015 |
| Tradex Supplies Ltd | Wholesale & retail | 2023 |
| Trailcourt Industries L.P. | | 2017 |
| Train Media Ltd | Information & communication | 2025 |
| Train Trans Ltd | Transport & logistics | 2016 |
| Train Tranz Ltd | Transport & logistics | 2019 |
| Trainor Bros Retail Limited | Wholesale & retail | 2015 |
| Trainor Investments Ltd | Real estate | 2025 |
| Trainor Medical Ltd | Health & social care | 2015 |
| Trainor's Limited | Hospitality | 2010 |
| Trainor's Trading Ltd | Hospitality | 2020 |
| Trans Europe Express Limited | Transport & logistics | 1990 |
| Transbridge Overseas L.P. | | 2015 |
| Transco Waste Limited | Water & waste | 2002 |
| Transcold Refrigeration Ltd | Manufacturing | 2014 |
| Transform 2 Xelente Ltd | Wholesale & retail | 2025 |
| Transform Digital Solutions Ltd | Information & communication | 2025 |
| TRANSFORM12 Limited | Arts & recreation | 2025 |
| Transmax Exort L.P. | | 2017 |
| Trappot NI Limited | Wholesale & retail | 2014 |
| Travel 4 ALL C.I.C. | Transport & logistics | 2010 |
| Travellers Secrets Limited | Administrative & support | 2002 |
| Travers Steel Limited | Manufacturing | 2007 |
| Treanor Safety Ltd | Professional & scientific | 2026 |
| Treasure House Kilkeel Ltd | Hospitality | 2025 |
| Tree Care N I Ltd | Administrative & support | 2019 |
| Trenao Ltd | Construction | 2009 |
| Trenta Limited | Wholesale & retail | 2018 |
| Trevor Annett Haulage Ltd | Transport & logistics | 2019 |
| Trevor Graham & Sons Limited | Construction | 2012 |
| Trevor Hill Limited | Construction | 1996 |
| Trevs Information & Technology Services Limited | Information & communication | 2020 |
| Tribeca Solutions Ltd | Real estate | 2014 |
| Tricam Caravans Limited | Wholesale & retail | 2019 |
| Tricel Composites (NI) Limited | Wholesale & retail | 1997 |
| Trident Manufacturing UK Ltd | Manufacturing | 2020 |
| Trim-Tech Graphics Ltd | Manufacturing | 2016 |
| Trimtrading Limited | Wholesale & retail | 2022 |
| Trinity Brickworks Ltd | Construction | 2019 |
| Trinity Candles Limited | Wholesale & retail | 2008 |
| Trinity Holdings Eire Limited | Agriculture & fishing | 2019 |
| Triple Eight Proteins Limited | Wholesale & retail | 2009 |
| Trona Products UK Ltd | Hospitality | 2021 |
| Tronbridge Worldwide L.P. | | 2017 |
| Trong UY 2003 Ltd | Other services | 2026 |
| Troughton Engineering Aircraft Maintenance Limited | Manufacturing | 2010 |
| Truck Hire European Ltd | Transport & logistics | 2014 |
| Truckserv (NI) Ltd | Wholesale & retail | 2013 |
| Truecore Limited | Professional & scientific | 2022 |
| Truesdale Paddock & Grassland Ltd | Agriculture & fishing | 2025 |
| Trustbuild Furniture Ltd | Wholesale & retail | 2025 |
| TSG Signs & Graphics Limited | Wholesale & retail | 2018 |
| Tsni Limited | Professional & scientific | 2024 |
| Ttnxs Limited | Wholesale & retail | 2025 |
| TTS Plumbing and Heating Ltd | Construction | 2016 |
| TTS Property Ltd | Real estate | 2023 |
| Tubular Ltd | Professional & scientific | 2022 |
| Tudor Blinds Retail Ltd | Manufacturing | 2015 |
| Tullurgan Enterprises Ltd | Real estate | 2021 |
| Tullyah Mechanical Limited | Construction | 2024 |
| Tullyard Plant Sales Ltd | Wholesale & retail | 2022 |
| Tullybridge Electrical Ltd | Construction | 2014 |
| Tullybridge Limited | Construction | 2014 |
| Tullybrook Ltd | Real estate | 2008 |
| Tullygarvan Plumbing and Heating Ltd | Construction | 2018 |
| Tullyglass Holdings Ltd | Extraterritorial | 2016 |
| Tullymacrieve Ltd | Extraterritorial | 2012 |
| Tullymurry House Limited | Hospitality | 2017 |
| Tullynagardy House Management Company Limited | Households | 2020 |
| Tullyvallen Rangers FC Community Limited | Arts & recreation | 2012 |
| Tullywinney Developments Limited | Construction | 2024 |
| Tullywinney Farms Ltd | Agriculture & fishing | 2021 |