| Ashgrove Farm Management (NI) Limited | Extraterritorial | 2004 |
| Ashkiss Solutions Limited | Health & social care | 2024 |
| Ashlain PVT Limited | Construction | 2025 |
| Ashleigh Court Apartments Management (Belfast) Limited | Households | 1991 |
| Ashleigh Manor Services Limited | Households | 1988 |
| Ashley Avenue Management Company Ltd | Households | 2007 |
| Ashley Crooks Consulting Ltd | Professional & scientific | 2018 |
| Ashley Crooks Properties Ltd | Real estate | 2023 |
| Ashley Maintenance Limited | Households | 1984 |
| Ashley Property Management Company Limited | Households | 2004 |
| Ashludie Trading Ltd | Wholesale & retail | 2014 |
| Ashraf Sokker Limited | Health & social care | 2014 |
| Ashton Community Trust | Administrative & support | 1998 |
| Ashton Decorators Limited | Other services | 2020 |
| Ashton Fraser Investments | Financial services | 2014 |
| Ashton Manor Limited | Households | 2000 |
| Ashton Recruitment Limited | Administrative & support | 2006 |
| Ashwood Agencies Limited | Hospitality | 1984 |
| Ashwood Commercial Finance LLP | | 2024 |
| Ashwood Veterinary Ltd | Professional & scientific | 2012 |
| Asia MIX Cuisine Ltd | Hospitality | 2022 |
| Asia Supermarket | Wholesale & retail | 2012 |
| Asian Foods Belfast Ltd | Hospitality | 2024 |
| Asian MIX Kitchen Restaurant Limited | Hospitality | 2024 |
| Asian MIX Store Limited | Wholesale & retail | 2019 |
| Asian Station Belfast Ltd | Wholesale & retail | 2020 |
| Asian Station Ltd | Wholesale & retail | 2019 |
| Asian WOK Limited | Hospitality | 2023 |
| Asidua Holdings Limited | Extraterritorial | 2007 |
| Asity Ltd | Professional & scientific | 2026 |
| ASK Holmes Limited | Information & communication | 2022 |
| Asklytics Ltd | Information & communication | 2025 |
| ASL Group UK Ltd | Manufacturing | 2023 |
| Aslam UK Pro Ltd | Wholesale & retail | 2024 |
| Asmaira Food Ltd | Hospitality | 2024 |
| Asme Instruments Limited | Professional & scientific | 2025 |
| ASN Pharma Ltd | Wholesale & retail | 2021 |
| ASO Kenny Ltd | Health & social care | 2023 |
| Aspect Media N. Ireland Ltd | Professional & scientific | 2013 |
| Aspen Enterprises (N.I.) Ltd | Real estate | 2025 |
| Aspen Healthcare Developments Limited | Financial services | 2026 |
| Aspen Holdings & Investments Ltd | Financial services | 2025 |
| Aspen View Management Company Ltd | Households | 2007 |
| Aspire 2 Achieve (Bespoke Services) Ltd | Education | 2018 |
| Aspire Achievers Ltd | Wholesale & retail | 2025 |
| Asqes PVT Limited | Information & communication | 2026 |
| ASR Properties (Belfast) Ltd | Real estate | 2022 |
| Assess Ireland Limited | Professional & scientific | 2020 |
| Asset Compliance and Risk Management Limited | Professional & scientific | 2019 |
| Assisi Pet Care (Northern Ireland) Limited | Manufacturing | 2025 |
| Assist Fleet Solutions Ltd | Wholesale & retail | 2025 |
| Associated Business Services Ltd | Information & communication | 1998 |
| Associated Processors Limited | Manufacturing | 1984 |
| Association of Related Churches (Ireland) | Other services | 2014 |
| Assurant Co. (NI), Ltd | Wholesale & retail | 2022 |
| Assure and Secure Limited | Administrative & support | 2021 |
| Assured Sports Ltd | Wholesale & retail | 2025 |
| Assured Supplements Ltd | Health & social care | 2023 |
| Asta's Glam Factory Limited | Other services | 2012 |
| Astbia Limited | Wholesale & retail | 2026 |
| Astiken Limited | Administrative & support | 1998 |
| Aston Phoenix Developments Ltd | Real estate | 2024 |
| Astonjdw Ltd | Administrative & support | 2023 |
| Astoria Business Limited | Professional & scientific | 2020 |
| Astracode Limited | Information & communication | 2025 |
| Astral (NI) Limited | Financial services | 2014 |
| Astral FOX Limited | Transport & logistics | 2020 |
| Astral Heating Training and Consultancy Limited | Construction | 2020 |
| Astrellar Limited | Arts & recreation | 2018 |
| Astuarin Commerce Ltd | Information & communication | 2026 |
| AT the Touch of a Button Ltd | Information & communication | 2013 |
| AT Wits END Ltd | Hospitality | 2018 |
| Atalla Areej H a Ltd | Wholesale & retail | 2025 |
| Atatech Electronics Limited | Wholesale & retail | 2025 |
| ATB Executive Travel Ltd | Administrative & support | 2023 |
| ATD Diagnostics Ltd | Health & social care | 2026 |
| Atddo Technology Company Limited | Wholesale & retail | 2024 |
| Atelier House Management Limited | Real estate | 2021 |
| Atelier-Design Limited | Professional & scientific | 2014 |
| Athangeon Ltd | Wholesale & retail | 2025 |
| Athena House Enterprise Limited | Real estate | 2019 |
| Athena Property Services Ltd | Real estate | 2021 |
| Athir Retail Ltd | Wholesale & retail | 2024 |
| Athlacca East Garryfine Ltd | Wholesale & retail | 2023 |
| Athletes 5 in 1 Ltd | Wholesale & retail | 2026 |
| Athletics Northern Ireland (2008) | Arts & recreation | 2006 |
| Athlyft Active Ltd | Wholesale & retail | 2026 |
| Athlyft Ltd | Wholesale & retail | 2025 |
| Athru Limited | Information & communication | 2025 |
| ATJ Young Ltd | Construction | 2026 |
| Atkco Limited | Professional & scientific | 2017 |
| Atkinson & Connolly Property Limited | Real estate | 2024 |
| Atlantes Holdings Limited | Information & communication | 2025 |
| Atlantic Biosciences Limited | Professional & scientific | 2021 |
| Atlantic Boba Ltd | Wholesale & retail | 2026 |
| Atlantic Exploit Labs Ltd | Information & communication | 2025 |
| Atlantic Facilities & Maintenance Ltd | Administrative & support | 2019 |
| Atlantic Partners Ltd | Information & communication | 2019 |
| Atlantic Ventures Holdings NI Limited | Professional & scientific | 2015 |
| Atlantic Youth Trust | Education | 2015 |