| Lisa Black Architecture Ltd | Professional & scientific | 2025 |
| Lisadian Agri Limited | Professional & scientific | 2005 |
| Lisburn Pharma Limited | Real estate | 2018 |
| Liscalgot Developments Ltd | Construction | 2002 |
| Liscor Ltd | Professional & scientific | 2024 |
| Lisfield Farms Ltd | Agriculture & fishing | 2021 |
| Lisfield Holdings Ltd | Administrative & support | 2020 |
| Lisheen 45 Limited | Financial services | 2026 |
| Lisleitrim Plant Ltd | Construction | 2022 |
| Lismore Professional Ltd | Wholesale & retail | 2024 |
| Lisnagree Ltd | Agriculture & fishing | 2016 |
| Lisnavale Management Company Limited | Households | 2009 |
| Lisraw Farming Ltd | Agriculture & fishing | 2014 |
| Lissanna Fuels Ltd | Wholesale & retail | 2017 |
| Lissavery Limited | Professional & scientific | 2023 |
| Lissbrak Direct Ltd | Wholesale & retail | 2020 |
| Lissize Electrical Ltd | Construction | 2020 |
| Litebite Protein Ltd | Manufacturing | 2023 |
| Lito LT Ltd | Manufacturing | 2024 |
| Little Blossom Boutique Ltd | Wholesale & retail | 2023 |
| Little Brother Productions Ltd | Information & communication | 2026 |
| Little Explorers Day Care & After School Ltd | Health & social care | 2019 |
| Little Explorers Daycare & Afterschool (Culloville) Ltd | Health & social care | 2020 |
| Little Goat Ltd | Information & communication | 2025 |
| Little Oak Developments Limited | Construction | 2006 |
| Little Paws for Coffee Ltd | Wholesale & retail | 2025 |
| Little Penny Thoughts Ltd | Wholesale & retail | 2017 |
| Little Treasures Kilkeel Ltd | Health & social care | 2017 |
| Littleoak Abbey SPV Limited | Construction | 2021 |
| Littleoak Property Limited | Extraterritorial | 2015 |
| Liviron Ltd | Wholesale & retail | 2024 |
| LM Play Limited | Financial services | 2025 |
| LMB Developments Ltd | Construction | 2026 |
| Lmcc Holdings Limited | Financial services | 2022 |
| LMP Controls Ltd | Manufacturing | 2003 |
| LMW Contracts Ltd | Administrative & support | 2021 |
| LNC Capital Limited | Real estate | 2024 |
| Lobol Limited | Extraterritorial | 2025 |
| Lock-Hart Environmental Ltd | Water & waste | 2010 |
| Lodestone Properties Limited | Real estate | 2018 |
| Logik Green Ltd | Professional & scientific | 2014 |
| LOK Electrical Ltd | Construction | 2020 |
| Loki Holdings Limited | Financial services | 2017 |
| Londberg Business L.P. | | 2016 |
| Long Acre Haulage Ltd | Manufacturing | 2025 |
| Longan Properties LP | | 2017 |
| Longlex Capital L.P. | | 2017 |
| Longmore Trading Limited | Wholesale & retail | 2005 |
| Longwood Park Limited | Real estate | 2022 |
| Loopland Estates Limited | Real estate | 1965 |
| Lorelei Investments Limited | Financial services | 2024 |
| Lough & Quay Bedrooms Ltd | Hospitality | 2014 |
| Lough FOY Limited | Wholesale & retail | 2024 |
| Lough Ross Trading Limited | Wholesale & retail | 2019 |
| Loughbracken Properties Limited | Real estate | 2023 |
| Loughbrook GXP Ltd | Professional & scientific | 2013 |
| Loughran Brewers Select Limited | Wholesale & retail | 2020 |
| Loughran Concrete Ltd | Mining & quarrying | 2014 |
| Loughran Contracts Ltd | Construction | 2016 |
| Loughview Mechanical Limited | Construction | 2020 |
| Louise Forsythe Eyecare Limited | Health & social care | 2026 |
| Lowe Medical Limited | Health & social care | 2011 |
| Lowtrans Impex L.P. | | 2017 |
| Loxztech Ltd | Extraterritorial | 2025 |
| LPI (N.I.) Limited | Real estate | 2005 |
| LQ Electrical Ltd | Construction | 2025 |
| LSG Transit L.P. | | 2015 |
| Ltcreative Tours Ltd | Administrative & support | 2020 |
| Ltfm Ireland Ltd | Real estate | 2023 |
| Lu-Bit Limited | Wholesale & retail | 2003 |
| Luca Digital Ltd | Information & communication | 2026 |
| Lucas BIO Thermo Validation Services Ltd | Professional & scientific | 2023 |
| Lucent Commerce LP | | 2017 |
| Lucerne Management Company Newry Limited | Extraterritorial | 2014 |
| Luganure Limited | Real estate | 2015 |
| Luke Curran & Co Ltd | Professional & scientific | 2016 |
| Luke Murphy Ltd | Wholesale & retail | 2015 |
| Lukella Business Consultancy Ltd | Professional & scientific | 2022 |
| Lulomi Limited | Wholesale & retail | 2024 |
| Lumen Cortex Limited | Information & communication | 2025 |
| Lumiere Productions Limited | Information & communication | 2007 |
| Luna Boutique Ltd | Wholesale & retail | 2022 |
| Lunar Property Holdings Limited | Real estate | 2021 |
| Lurgan Demesne Limited | Households | 2016 |
| Luton Trading LP | | 2017 |
| Luxe Bathrooms Ireland Ltd | Wholesale & retail | 2020 |
| Luxe Scenses Ltd | Wholesale & retail | 2025 |
| Luxeso Ltd | Wholesale & retail | 2022 |
| Lynch Auto Sales Ltd | Wholesale & retail | 2026 |
| Lynch Cars Ltd | Wholesale & retail | 2018 |
| Lynch Financial Services Ltd | Financial services | 2020 |
| Lynch Ventures Ltd | Administrative & support | 2024 |
| Lyphard Creek Ltd | Wholesale & retail | 2025 |
| M & E Painting Contracts Ltd | Construction | 2025 |
| M & E Services (N.I.) Limited | Construction | 2018 |
| M & H Daly Property Limited | Real estate | 2011 |
| M & M Carpentry & Fitout Limited | Construction | 2020 |
| M & M Plant Hire Limited | Administrative & support | 2008 |
| M & M Trucks & Spares Ltd | Transport & logistics | 2000 |
| M a B Groundworks Ltd | Construction | 2015 |