| A&L Wallace Limited | Health & social care | 2016 |
| A&M for U Ltd | Professional & scientific | 2024 |
| A&P Drives Ltd | Construction | 2025 |
| A&R Belfast Ltd | Professional & scientific | 2016 |
| A&S Faith Development Ltd | Other services | 2025 |
| A&S Property Investments Limited | Real estate | 2023 |
| A&S Roof Repairs Ltd | Construction | 2021 |
| A-Futms Ltd | Information & communication | 2025 |
| A-Mech N.I. Limited | Construction | 2022 |
| A-Star Carpentry & Joinery Ltd | Construction | 2023 |
| A. Bates Skip Hire Limited | Extraterritorial | 1996 |
| A. Hutchinson (Floor and Wall Supplies) Limited | Wholesale & retail | 1977 |
| A. Q. Properties Limited | Real estate | 1987 |
| A.& C. Electric, Limited | Construction | 1952 |
| A.A. Dunlop Limited | Construction | 2007 |
| A.A. Dunlop NO. 2 Ltd | Construction | 2025 |
| A.Afr Ltd | Health & social care | 2025 |
| A.B. Distributors Limited | Wholesale & retail | 1971 |
| A.C.J. Trading Limited | Energy | 2003 |
| A.Frank Group Limited | Professional & scientific | 2024 |
| A.G. Newberry Limited | Wholesale & retail | 1982 |
| A.G.S.S. NI Limited | Energy | 2023 |
| A.I. Locksmith Service Ltd | Administrative & support | 2016 |
| A.M. Custom Clothing (EU) Limited | Wholesale & retail | 2025 |
| A.M. Removals Ltd | Transport & logistics | 2025 |
| A.O.D. Fishing Ltd | Agriculture & fishing | 2016 |
| A.P.L. Developments Ltd | | 2004 |
| A.S. & D. Enterprises Limited | | 1963 |
| A.S. & D. Enterprises Ltd | | 2004 |
| A.S. Residential LLP | | 2014 |
| A.Steede & Co. Limited | Extraterritorial | 1971 |
| A.W.S . Group (N.I.) Ltd | Information & communication | 2023 |
| A1 Ace Bates Skip Hire Limited | Extraterritorial | 1997 |
| A1 Bates Bros. Skip Hire Limited | Extraterritorial | 1997 |
| A1 Batesy Skip Hire Limited | Extraterritorial | 1997 |
| A1 Groundworks Belfast Ltd | Construction | 2023 |
| A1 Hosts Limited | Real estate | 2022 |
| A1 Pointers Ltd | Construction | 2026 |
| A1 Solutions (NI) Limited | Wholesale & retail | 2007 |
| A1 Solutions Retail Ltd | Wholesale & retail | 2018 |
| A1 Top Soil Supplies Ltd | Extraterritorial | 2011 |
| A100 Security Service Limited | Administrative & support | 2023 |
| A2B Cabs (2015) Limited | Transport & logistics | 2015 |
| A2B Storage & Distribution Ltd. | Transport & logistics | 2010 |
| A2B Transport 2022 Ltd | Transport & logistics | 2022 |
| A2Z Caters Limited | Hospitality | 2019 |
| A2Z Mobile Accessories Ltd | Wholesale & retail | 2021 |
| A2Z-CM UK Limited | Professional & scientific | 2013 |
| A4 Property Ltd | Real estate | 2023 |
| A8 Autos Limited | Wholesale & retail | 2025 |
| AA Buff Ltd | Wholesale & retail | 2025 |
| AA Specialists Ltd | Construction | 2024 |
| AA Veterans Support | Other services | 2011 |
| AAA Real Estate Services Limited | Real estate | 2018 |
| Aadhi Limited | Information & communication | 2013 |
| Aadvantage Services Ltd | Construction | 2021 |
| Aagoshh Belfast Limited | Construction | 2025 |
| Aakiho Ltd | Wholesale & retail | 2023 |
| Aalpha Solutions Ltd | Professional & scientific | 2024 |
| Aamen Ltd | Professional & scientific | 2023 |
| Aapta Nutrifoods Ltd | Manufacturing | 2025 |
| Aaron Clark Limited | Wholesale & retail | 2025 |
| Aaron Heaney Hair Ltd | Other services | 2015 |
| Aaron MCG Consulting Ltd | Professional & scientific | 2025 |
| Aaronmurphy Ltd | Construction | 2025 |
| Aartius Management Solutions Limited | Professional & scientific | 2016 |
| Aaruhitech Ltd | Information & communication | 2018 |
| Aarvic Tech Limited | Information & communication | 2025 |
| Aashvah Limited | Information & communication | 2019 |
| Aayat Properties Ltd | Real estate | 2024 |
| AAZ Group Limited | Administrative & support | 2019 |
| AB Credit Services Limited | Professional & scientific | 2016 |
| AB Events Media Ltd | Professional & scientific | 2020 |
| AB Fulfillment Ltd | Wholesale & retail | 2023 |
| AB Global Media Ltd | Wholesale & retail | 2026 |
| AB Inbev Ireland Limited | Extraterritorial | 1951 |
| AB Residential Properties Limited | Real estate | 2016 |
| AB5 Social Limited | Professional & scientific | 2026 |
| ABA Homes Ltd | Real estate | 2026 |
| Abaco Developments LLP | | 2006 |
| Abacus Central Systems Limited | Information & communication | 2000 |
| Abacus Legal Recruitment Limited | Administrative & support | 2004 |
| Abacus Professional Recruitment Limited | Administrative & support | 2003 |
| Abacus Talent Group Limited | Professional & scientific | 2018 |
| Abafoteq Ltd | Information & communication | 2023 |
| Abasin Linguistic Services Limited | Professional & scientific | 2025 |
| Abba Driver Training Services Limited | Administrative & support | 2014 |
| Abbey Caravans & Leisure Ltd | Wholesale & retail | 2005 |
| Abbey Gymnastics C.I.C. | Arts & recreation | 2010 |
| Abbey Joinery & Shopfitting Ltd | Construction | 2012 |
| Abbey Judo Club Limited | Arts & recreation | 2022 |
| Abbey Repointing Ltd | Construction | 2026 |
| Abbey Tiles & Bathrooms Ltd | Wholesale & retail | 2025 |
| Abbey Tiles Limited | Construction | 2019 |
| Abbeycourt Apartments Limited | Real estate | 1984 |
| Abbeydale (Ards) Management Limited | Households | 2019 |
| Abbeyfield Belfast Society Limited the | Health & social care | 1960 |
| Abbeyleigh Management Company Ltd | Real estate | 2018 |
| Abbeyvale Group Limited | Real estate | 2023 |
| Abbicoil Springs Limited | Manufacturing | 1957 |