| Linley Properties Limited | Real estate | 1990 |
| Linsfort Bay Enterprises (NI) Limited T/A Mclaughlin Concrete Flooring Limited | Construction | 2021 |
| Lintel Consulting Limited | Professional & scientific | 2005 |
| Lisahally Ltd | Real estate | 2011 |
| Lisnagelvin Merchants Association Limited | Administrative & support | 1983 |
| Little Acorns Community Pre-School | Education | 1998 |
| Little BGC Ltd | Hospitality | 2019 |
| Little Kitten Childcare Ltd | Health & social care | 2024 |
| Little Timeouts Limited | Manufacturing | 2022 |
| Live @ the Square Ltd | Arts & recreation | 2021 |
| LJ3 Ltd | Wholesale & retail | 2026 |
| LK Auto Salvage NI Ltd | Wholesale & retail | 2026 |
| Lmho Ltd | Hospitality | 2024 |
| LMI Safety Ltd | Professional & scientific | 2019 |
| Lmpd Limited | Manufacturing | 2014 |
| LNB Homes Ltd | Real estate | 2021 |
| LNB Property Investments Ltd | Real estate | 2024 |
| LNC Enterprises Ltd | Manufacturing | 2015 |
| LNG (CG) Ltd | Real estate | 2017 |
| LNT Investments Ltd | Real estate | 2018 |
| LO & SLO Group Ltd | Hospitality | 2024 |
| Lockadesign Ltd | Professional & scientific | 2025 |
| Logical Solutions Ireland Ltd | Manufacturing | 2006 |
| Logistics Plus Ireland Limited | Transport & logistics | 2024 |
| Loinnir Ltd | Other services | 2018 |
| LOK Assets Ltd | Real estate | 2024 |
| London Street Projects Ltd | Real estate | 2022 |
| Londonderry Chamber of Commerce (Incorporated) | Other services | 1885 |
| Londonderry Inner City Trust | Other services | 1987 |
| Longs Farm Shop Campsie Ltd | Wholesale & retail | 2022 |
| Longs Farm Shop Springtown Ltd | Wholesale & retail | 2022 |
| Lorna O'Donnell Limited | Professional & scientific | 2020 |
| Lottawood Limited | Real estate | 2018 |
| Lough Enagh Motel Limited | Extraterritorial | 1974 |
| Lough Foyle Farm Estates Limited | Real estate | 1976 |
| Lough Foyle Fishing Company Limited | Agriculture & fishing | 2014 |
| Lough Shore Joinery Limited | Manufacturing | 2020 |
| Loughrey & Chada Physio NI Limited | Health & social care | 2023 |
| Loughview Safety Limited | Professional & scientific | 2025 |
| Louise Kate Ltd | Wholesale & retail | 2024 |
| Love Umbria Limited | Arts & recreation | 2008 |
| Lovegym Athleisure Ltd | Wholesale & retail | 2025 |
| Lower Liberties Oyster Company Ltd | Agriculture & fishing | 2021 |
| LPI Portfolio Ltd | Real estate | 2024 |
| LSE 1 Properties Limited | Real estate | 2025 |
| LSR Holdings Limited | Real estate | 2019 |
| LSS Limited | Wholesale & retail | 2003 |
| LT56 Trading Limited | Real estate | 2020 |
| Ltbe Ltd | Other services | 2019 |
| Luca Enterprises Limited | Real estate | 2024 |
| Lucalibro Limited | Information & communication | 2025 |
| Lucid Interactive Ltd | Information & communication | 2002 |
| Ludden Construction Limited | Financial services | 2019 |
| Luham Developments Limited | Real estate | 2015 |
| Lumen Healthcare Ltd | Public administration | 2021 |
| Lumenedge Technologies Ltd | Information & communication | 2023 |
| Lumos Holding Limited | Financial services | 2026 |
| Lunalilu Limited | Wholesale & retail | 2025 |
| Lusso Skin Ltd | Other services | 2022 |
| LUX Recover Ltd | Other services | 2023 |
| Luxe Lengths Limited | Other services | 2019 |
| Luxury Tiny Homes Ltd | Manufacturing | 2023 |
| Luxurybuyuk Limited | Wholesale & retail | 2026 |
| Lynch Builders Ltd | Construction | 2025 |
| Lynch Civils Ltd | Construction | 2019 |
| Lynch Electrical North West Limited | Construction | 2019 |
| Lynch's Foodstores (Holdings) Limited | Financial services | 2014 |
| Lynwood Homes Limited | Construction | 1981 |
| M & E Electrical (N.I.) Ltd | Construction | 2016 |
| M & J Devlin Limited | Construction | 2025 |
| M & L Contracts (NI) Ltd | Construction | 2013 |
| M & L Mechanical Engineering Ltd | Construction | 2019 |
| M & M Contracts (N.I) Ltd | Construction | 2021 |
| M a Mccloskey Limited | Professional & scientific | 2011 |
| M Cunning Haulage Ltd | Transport & logistics | 2025 |
| M D Vehicle Hire Ltd | Administrative & support | 2022 |
| M Doherty Wood Products Limited | Manufacturing | 2019 |
| M E & a Property Ltd | Real estate | 2023 |
| M&D Contracts Ltd | Construction | 2021 |
| M-Presa Ltd | Real estate | 2025 |
| M.I.W.I Services Limited | Manufacturing | 2022 |
| MAC Brickwork and Construction Ltd | Construction | 2024 |
| Macan Developments Limited | Construction | 2004 |
| Macc ANN Trading Co. 2 Ltd | Wholesale & retail | 2019 |
| Macfearchair Electrical Limited | Mining & quarrying | 2018 |
| Macglen KL Ltd | Wholesale & retail | 2015 |
| Macha Safe Ltd | Wholesale & retail | 2025 |
| Mack Scaffolding Services Ltd | Construction | 2018 |
| Macm Assets Ltd | Real estate | 2026 |
| Mactac Ltd | Real estate | 2021 |
| Madame PHO Derry Ltd | Hospitality | 2025 |
| Maddox Projects Ltd | Real estate | 2016 |
| Maddybenny Riding Centre and Stud Limited | Education | 2002 |
| Made Medics Ltd | Health & social care | 2026 |
| Madingo Limited | Other services | 2002 |
| Magee Financial Limited | Financial services | 2024 |
| Magheraboy Developments Limited | Construction | 2010 |
| Maghon Property Forensics Ltd | Construction | 2017 |
| Magic Chef Limited | Hospitality | 2025 |
| Magim Limited | Real estate | 2013 |