| Acff Consulting Ltd | Manufacturing | 2022 |
| Acheson Estate Ltd | Households | 2025 |
| Acheson Homes Limited | Construction | 2007 |
| Achievers Excel Limited | Professional & scientific | 2000 |
| Acis (NI) Ltd | Wholesale & retail | 2014 |
| ACK Productions Limited | Arts & recreation | 2009 |
| Ackhurst Limited | Wholesale & retail | 2008 |
| Aclhemy Distil Ltd | Wholesale & retail | 2023 |
| Acme Ideas (22) Limited | Arts & recreation | 2020 |
| Acme Ideas Limited | Arts & recreation | 2004 |
| Acorn Developments (NI) Ltd | Construction | 2004 |
| Acorn Film & Video Ltd | Information & communication | 1996 |
| Acorn Holdco II Limited | Information & communication | 2020 |
| Acorn Holdco Ltd | Information & communication | 2020 |
| Acornhill Management Company Limited | Households | 2002 |
| Acoustic Fire Seal Ltd | Construction | 2014 |
| ACP WNI Limited | Energy | 2016 |
| Acquiring Solutions Ltd | Financial services | 1998 |
| Acre NI Consultancy Limited | Professional & scientific | 2026 |
| Acrefield Properties Management Company Limited | Real estate | 2006 |
| Acrewood Daycare CIC | Health & social care | 2022 |
| Acrobatic Software Limited | Information & communication | 1999 |
| Acromion Ltd | Health & social care | 2024 |
| Across Borders Consulting Limited | Professional & scientific | 2020 |
| Across Borders Study Limited | Education | 2015 |
| ACS Control Systems Limited | Administrative & support | 1992 |
| ACS Property Development Ltd | Real estate | 2025 |
| ACS Wind Care Limited | Administrative & support | 2013 |
| ACT 4 Solutions Limited | Professional & scientific | 2008 |
| ACT NOW Limited | Other services | 2023 |
| ACT Venture Capital (N.I.) Limited | Financial services | 1994 |
| Actava Ltd | Manufacturing | 2025 |
| Actavo (Northern Ireland) Limited | Administrative & support | 2011 |
| Action Cancer | Health & social care | 1985 |
| Action Deaf Youth | Other services | 2013 |
| Action for Children (Northern Ireland) Ltd | Health & social care | 2016 |
| Action for Community Transformation Initiative | Other services | 2012 |
| Action Renewables | Other services | 2003 |
| Action Renewables Energy Trading Limited | Professional & scientific | 2010 |
| Action Tech Limited | Manufacturing | 2020 |
| Actium Online Ltd | Information & communication | 2025 |
| Active CLO Ltd | Wholesale & retail | 2025 |
| Active Money Solutions Ltd | Financial services | 2012 |
| Active Voice Psychological Services Ltd | Health & social care | 2020 |
| Active WOK Ltd | Hospitality | 2026 |
| Activescan Limited | Information & communication | 2023 |
| Activon Impex Limited | Manufacturing | 2026 |
| Activtransport Limited | Administrative & support | 2021 |
| Actons Restaurant Limited | Extraterritorial | 1985 |
| Actradingni Ltd | Wholesale & retail | 2025 |
| Acts (Africa Christian Textbooks) International | Other services | 2025 |
| Acturius UK Ltd | Wholesale & retail | 2025 |
| Acumen Developments Limited | Real estate | 1997 |
| AD Energy (NI) Limited | Manufacturing | 2014 |
| AD Enterprises (Northern Ireland) Limited | Construction | 2006 |
| AD Services Ltd | Transport & logistics | 2022 |
| ADA Creative Studios Ltd | Professional & scientific | 2025 |
| Adair Properties N.I Ltd | Real estate | 2024 |
| Adairco Ltd | Hospitality | 2015 |
| Adam AKE Limited | Wholesale & retail | 2024 |
| Adam Derik 1978 Ltd | Other services | 2026 |
| Adam Morgan Technology Ltd | Information & communication | 2024 |
| Adams Mcgillan & Company Ltd | Real estate | 2015 |
| Adams-Social-Marketing Ltd | Wholesale & retail | 2025 |
| Adamson Refrigeration Contracts Ltd | Manufacturing | 2019 |
| Adapt Belfast Ltd | Health & social care | 2026 |
| Adapt Group Dundonald Ltd | Health & social care | 2026 |
| Adaptek Limited | Information & communication | 2020 |
| Adarra Developments Limited | Real estate | 1998 |
| Adbox Industries Limited | | 2004 |
| ADC Entertainments (N.I.) Limited | Wholesale & retail | 2015 |
| Added Value Management Limited | Real estate | 2015 |
| Addeelia Consultancy Limited | Professional & scientific | 2017 |
| Addeelia Management Company Limited | Extraterritorial | 2005 |
| Additude Creative Limited | Arts & recreation | 2008 |
| Addmineral Systems Ltd | Wholesale & retail | 2025 |
| Addni Limited | Education | 2009 |
| Addx International Ltd | Manufacturing | 2019 |
| ADE2CARE Healthcare Ltd | Health & social care | 2026 |
| Adelaide Enterprises Ltd | Real estate | 2022 |
| Adelaide Exchange Limited | Real estate | 2013 |
| Adelaide Property Investment Limited | Extraterritorial | 2015 |
| Adelaide Property Ltd | Real estate | 2025 |
| Adeline Hogg Ltd | Wholesale & retail | 2025 |
| Adepta Partners Ltd | Professional & scientific | 2024 |
| ADF Lifestyle Limited | Wholesale & retail | 2024 |
| ADG Property Ltd | Real estate | 2022 |
| ADH MOR Ltd | Professional & scientific | 2025 |
| Adhaus Media Ltd | Professional & scientific | 2002 |
| Adhear Services Ltd | Health & social care | 2023 |
| ADI Store Ltd | Information & communication | 2025 |
| Adia Rose Limited | Transport & logistics | 2026 |
| ADK Property Services Limited | Real estate | 2021 |
| ADL Tile & Stone Limited | Wholesale & retail | 2009 |
| Adliv Motors UK Ltd | Wholesale & retail | 2024 |
| Adln Solutions Ltd | Professional & scientific | 2021 |
| ADM Smile Ltd | Health & social care | 2025 |
| ADN (NI) Limited | Hospitality | 2011 |
| Adnan Online Sales Limited | Wholesale & retail | 2025 |
| Adonay Trade Limited | Wholesale & retail | 2024 |