| Cords Coventry Limited | Wholesale & retail | 1911 |
| Cork Tree Services Limited | Professional & scientific | 2019 |
| Corweld Engineering Ltd | Manufacturing | 2025 |
| Cosy Cwtch Stays Limited | Real estate | 2026 |
| CPA Construction Services Ltd | Construction | 2026 |
| Craftless Design Company Ltd | Extraterritorial | 2023 |
| Craig LFC5 Limited | Hospitality | 2021 |
| Crazy Joes Coffee Limited | Hospitality | 2026 |
| Crazy Joes Ltd | Hospitality | 2023 |
| Creative Hub Training Limited | Education | 2019 |
| Creative Landscaping & Driveways Ltd | Administrative & support | 2024 |
| Creative Martial Arts Limited | Information & communication | 2021 |
| Creative Signs Wales Ltd | Professional & scientific | 2017 |
| Cress-Tech Rail Solutions Ltd | Other services | 2021 |
| Crezzie Rail Limited | Construction | 2016 |
| Crosswoods Limited | Wholesale & retail | 1940 |
| Crown Tyre and Auto Centre Limited | Wholesale & retail | 2017 |
| CSJ Carpentry & Construction Ltd | Manufacturing | 2022 |
| CT Appliances Ltd | Manufacturing | 2020 |
| Cuplecoffee Limited | Hospitality | 2024 |
| Custom Workwear UK Limited | Wholesale & retail | 2021 |
| Cwcw Rail Limited | Construction | 2016 |
| CWM TAF Morgannwg Mind | Health & social care | 2008 |
| Cwmbach Chippy Ltd | Hospitality | 2026 |
| Cwrt Y Meistr Limited | Real estate | 2021 |
| Cyfarthfa Court Management Company Limited | Households | 2005 |
| Cyfarthfa Structures Limited | Water & waste | 2007 |
| Cymru Healthcare Supplies Limited | Wholesale & retail | 1998 |
| Cynffon Ltd | Information & communication | 2026 |
| D & a Doors Limited | Manufacturing | 2014 |
| D & M Wholesale SW Limited | Wholesale & retail | 2026 |
| D & T Rees Holdings Limited | Real estate | 2018 |
| D B Phillips Estate Agents Limited | Real estate | 2014 |
| D J Protheroe & Sons Limited | Other services | 2011 |
| D J Rees Decorating Services Limited | Construction | 2003 |
| D Wakeham Limited | Construction | 2019 |
| D&O Steelfixing Ltd | Construction | 2025 |
| D.A. Davies Foodstores Limited | Wholesale & retail | 2005 |
| D3 Digital Services Limited | Information & communication | 2015 |
| Daet Limited | Transport & logistics | 2025 |
| Daleon Fitness Limited | Arts & recreation | 2014 |
| Dani’S Hair and Beauty Studio Ltd | Other services | 2025 |
| Danny Electrical Services Limited | Construction | 2018 |
| Daray Properties Ltd | Real estate | 2025 |
| Darganfod Safety and Training Ltd | Professional & scientific | 2025 |
| Darkos Barber Shop Limited | Other services | 2023 |
| David Rees Joinery Limited | Manufacturing | 2011 |
| Davs Kitchen Ltd | Hospitality | 2022 |
| Day’S Aircraft Services Limited | Manufacturing | 2023 |
| Ddraig Yoga Ltd | Education | 2025 |
| Ddsk Developments Limited | Construction | 2019 |
| Deft Business Consultants Limited | Administrative & support | 2023 |
| DEN Transport Limited | Transport & logistics | 2016 |
| Dery Limited | Other services | 2016 |
| Design and Manufacture Limited | Manufacturing | 1982 |
| Design Holdings Limited | Professional & scientific | 1998 |
| Deva Haulage Limited | Transport & logistics | 2018 |
| DFT Properties Ltd | Real estate | 2024 |
| Diagnose Dan's Service and Repairs Ltd | Wholesale & retail | 2026 |
| Digital Citizen Academy Ltd | Education | 2025 |
| Dino Fossils UK Ltd | Wholesale & retail | 2019 |
| Dirty Birdie Golf Goods Limited | Wholesale & retail | 2024 |
| Disperazol Pharma Limited | Professional & scientific | 2026 |
| Distinction Rigging and Electrical Ltd | Construction | 2020 |
| Diverse Productions Ltd | Arts & recreation | 2022 |
| Dizzy Heights Access Solutions Ltd | Construction | 2014 |
| DK Laser Ltd | Water & waste | 2026 |
| DLD Contractors Limited | | 2005 |
| DLM Groundwork Contractors Ltd | Construction | 2025 |
| Dmbm Movement Specialist Therapy Clinic Ltd | Health & social care | 2026 |
| DMR Investment Company Limited | Other services | 2007 |
| DNR247 Ltd | Transport & logistics | 2019 |
| Dogsden Day Care Ltd | Agriculture & fishing | 2020 |
| Door Centre South Wales Limited | Construction | 2025 |
| Doors 2 Go Ltd | Construction | 2019 |
| Dor-Master Ltd | Administrative & support | 2013 |
| Dowlais Crumbs Limited | Hospitality | 2014 |
| Dowlais Heating Ltd | Construction | 2002 |
| Dowlais Pharmacy Limited | Health & social care | 1997 |
| Dowlais RFC Limited | Arts & recreation | 2012 |
| Dowlais Stores Limited | Wholesale & retail | 2019 |
| DPH Architect Ltd | Professional & scientific | 2021 |
| DPX Security Ltd | Administrative & support | 2025 |
| DR Shepherd’S Hair & Health Clinic Ltd | Health & social care | 2026 |
| DR. Louise Aesthetics Ltd | Health & social care | 2022 |
| Dragon Labour Solutions Ltd | Administrative & support | 2025 |
| Dragonfly Print Ltd | Other services | 2014 |
| Draig Haulage Limited | Transport & logistics | 2004 |
| Draig Warehousing Limited | Transport & logistics | 2021 |
| Drec Building Ltd | Construction | 2014 |
| Drew Building Maintenance Limited | Construction | 2017 |
| DRH Business Systems Limited | Information & communication | 1993 |
| Drinks N Things Limited | Wholesale & retail | 2020 |
| DRT Media Limited | Information & communication | 2018 |
| DTL Groundworks & Civils Ltd | Construction | 2024 |
| Duai Ltd | Wholesale & retail | 2022 |
| Dubs Maintenance Limited | Construction | 2019 |
| Dukestown Projects Ltd | Construction | 2017 |
| Dvlm Steed Enterprises Ltd | Financial services | 2026 |
| DW Hynes Investments Limited | Financial services | 2026 |