| ALL Pipe Engineering Limited | Construction | 1994 |
| Allens at the Oaks Limited | Hospitality | 2021 |
| Alleycats Features - Lost Boys Ltd | Information & communication | 2019 |
| Allgo Engineering Supplies Limited | Wholesale & retail | 2008 |
| Allgo Mechanical Engineering Limited | Manufacturing | 2008 |
| Allspares Online Ltd | Wholesale & retail | 2023 |
| Alltradesni Ltd | Construction | 2026 |
| Allwall Partitions Limited | Construction | 2016 |
| Almafe Limited | Real estate | 2025 |
| Alno Markets Ltd | Information & communication | 2019 |
| Alodium Victoria Limited | Wholesale & retail | 2026 |
| Alpnet Solutions Limited | Information & communication | 2022 |
| ALT Contracts Ltd | Construction | 2023 |
| ALT Rentals Ltd | Real estate | 2025 |
| Altnagelvin Garden Centre Limited | Wholesale & retail | 2014 |
| Altura Promotions Ltd | Hospitality | 2025 |
| Always Towing Ltd | Wholesale & retail | 2025 |
| AM BAU UND Planung Ltd | Administrative & support | 2023 |
| Amalgam Properties Limited | | 2003 |
| Ambience Home Solutions Limited | Wholesale & retail | 2017 |
| Ambrosetti Properties Ltd | Real estate | 2024 |
| AMC Contracts & Sons Ltd | Construction | 2020 |
| Amcg Contracts Ltd | Construction | 2025 |
| Amelia Air Ventilation Ltd | Manufacturing | 2021 |
| AMF Consultancy Ltd | Construction | 2026 |
| Amphora Investments Limited | Real estate | 2017 |
| AMS - 22 Ltd | Wholesale & retail | 2022 |
| AN RÍ Contracts Limited | Professional & scientific | 2026 |
| Anahorish Music Ltd | Arts & recreation | 2017 |
| Anchor OIL Company Limited | Extraterritorial | 1995 |
| Ancs Consultancy Ltd | Information & communication | 2024 |
| Anderson Mcque Ltd | Administrative & support | 2020 |
| Andjeoynf Ltd | Wholesale & retail | 2024 |
| Andrei Hygiene Limited | | 2013 |
| Andrews Cardiology Limited | Health & social care | 2025 |
| Anduma Productions Ltd | Information & communication | 2018 |
| Anecom Ltd | Wholesale & retail | 2026 |
| Anewhouse Ltd | Real estate | 2025 |
| Anfinity Solutions Limited | Professional & scientific | 2020 |
| Anglesea Properties Ltd | Real estate | 2024 |
| ANN Baird Ltd | Hospitality | 2011 |
| Anncan Global Limited | Manufacturing | 2024 |
| Ansa Leisure Limited | Hospitality | 2020 |
| Anseoapparel Ltd | Wholesale & retail | 2025 |
| Antrim Coast Properties Limited | Households | 2025 |
| Anycake.Com Ltd | Wholesale & retail | 2013 |
| Aoer Holdings Limited | Financial services | 2025 |
| Aosh Limited | Real estate | 2025 |
| Apex Data & Economics Ltd | Information & communication | 2026 |
| Apsc Properties Ltd | Real estate | 2022 |
| Apto Technologies Ltd | Information & communication | 2016 |
| Aptrick Ltd | Administrative & support | 2016 |
| Aqua Leak Detection Services Ltd | Construction | 2021 |
| Aquaclean NW Ltd | Administrative & support | 2025 |
| Aquatec Sports Limited | Wholesale & retail | 2015 |
| Aquidigital Ltd | Information & communication | 2017 |
| ARA Workplace Law Limited | Administrative & support | 2023 |
| Aran Online Ltd | Wholesale & retail | 2018 |
| ARC Fitness Ltd | Other services | 2019 |
| Archive Ireland C.I.C. | Arts & recreation | 2024 |
| ARD Cluain Ltd | Financial services | 2024 |
| ARD Grange Management Company Limited | Households | 2003 |
| ARD NA GAL Limited | Construction | 2021 |
| Ardan Services Limited | Information & communication | 2023 |
| Ardisle Trading Limited | Wholesale & retail | 2018 |
| Ardkill Timber Frames Ltd | Construction | 2014 |
| Ardmore Community Development Group Ltd | Other services | 2025 |
| Ardmore Enterprises Limited | Hospitality | 2011 |
| Ardmore Flooring Company Ltd | Construction | 2006 |
| Ardmore Inns Ltd | Wholesale & retail | 2013 |
| Ardnalee Homes Ltd | Construction | 2023 |
| Ardress Limited | Professional & scientific | 1999 |
| Arion-Sigg Productions Ltd | Information & communication | 2026 |
| Arion-Sigg Tora-Gwen Productions Ltd | Information & communication | 2026 |
| Artarcadia Ltd | Arts & recreation | 2016 |
| Artists Live Limited | Information & communication | 2012 |
| ARTSPACE2 Ltd | Education | 2023 |
| Ascot Signs Ltd | Administrative & support | 2013 |
| Ashburn Image Clinic Limited | Other services | 2026 |
| Ashcool Ltd | Real estate | 2019 |
| Ashcroft Management Ltd | Real estate | 2016 |
| Ashfield Properties Guildhall Street Limited | Construction | 2018 |
| Ashmore Construction Services Limited | Construction | 2022 |
| ASI Architects Ltd | Professional & scientific | 2003 |
| Asian Foods MR Ltd | Wholesale & retail | 2024 |
| Asiko Architects Ltd | Professional & scientific | 2025 |
| Aspire Care Ireland Limited | Health & social care | 2023 |
| Assess IT Ltd | Financial services | 2021 |
| Assure (NW) Ltd | Administrative & support | 2025 |
| Astravo Ltd | Wholesale & retail | 2020 |
| Asylum Developments Ltd | Real estate | 2012 |
| Asylum Properties Limited | Real estate | 2023 |
| Atcheson & SON (Derry) Limited | Wholesale & retail | 2005 |
| ATL Assets Ltd | Real estate | 2024 |
| ATL Transport Ltd | Transport & logistics | 2006 |
| Atlantic Gateway Limited | Information & communication | 2016 |
| Atlantic Hub Energy Limited | Energy | 2020 |
| Atlantic Hub Limited | Information & communication | 2017 |
| Atlantic Hub Property Limited | Information & communication | 2017 |
| Atlantic Nutrition Ltd | Professional & scientific | 2011 |