| J Murray Services Ltd | Construction | 2017 |
| J.Barbour & Sons,Limited | Manufacturing | 1912 |
| J.R.Henderson(Transport & Storage)Limited | Real estate | 1963 |
| J.W. Haygarth Limited | Manufacturing | 1975 |
| Jade Developments (North East) Limited | Construction | 2006 |
| James E Baird (Solicitor) Limited | Professional & scientific | 2003 |
| JECB78 Limited | Health & social care | 2025 |
| JES Rented Properties Limited | Real estate | 2002 |
| Jesmond Nurseries Limited | Health & social care | 2000 |
| JMC Imports Limited | Other services | 2005 |
| JND Solutions Ltd | Information & communication | 2006 |
| Jobling of Sunderland (Holdings) Limited | Professional & scientific | 1978 |
| Joel Memorial Limited | Other services | 2003 |
| John Barnes Design Consultancy Limited | Professional & scientific | 2007 |
| John Moody & SON Limited | Construction | 1981 |
| Johnson's Painting Contractors Limited | Construction | 2003 |
| Joseph James Joinery Ltd | Construction | 2005 |
| Joyce-Loebl Group Limited | Extraterritorial | 1998 |
| Junella Fish Merchants and Catering Services Limited | Real estate | 1996 |
| Just ASK Denise Ltd | Administrative & support | 2024 |
| K & G Finlay Limited | Wholesale & retail | 2003 |
| K M Builders & Groundworks Ltd | Construction | 2007 |
| K. Murray (Building Services) Limited | Construction | 2003 |
| Katy Wilson Limited | Professional & scientific | 2024 |
| Kelevra Solutions Limited | Agriculture & fishing | 2007 |
| Kelly's DIY Limited | Wholesale & retail | 2003 |
| KEN Jobling Financial Planning Limited | Professional & scientific | 2003 |
| KEN Phillips Carpet Fitting Specialist Limited | Construction | 2003 |
| KES Solutions UK Limited | Administrative & support | 2007 |
| Keynsham Enterprises Limited | Information & communication | 2016 |
| King Neptune Restaurant Limited | Hospitality | 2000 |
| Kingston Sofas Ltd | Manufacturing | 2000 |
| Kingswood Court Management Company (Tynemouth) Limited | Households | 2002 |
| Kite I.T. Limited | Information & communication | 1997 |
| KNS Automotive Limited | Wholesale & retail | 1998 |
| Koziwarm Limited | Construction | 1988 |
| KRM Software Limited | Information & communication | 2007 |
| Krypton Electrical Wholesalers Limited | Wholesale & retail | 2005 |
| KS Electrical Management Services Ltd | Professional & scientific | 2024 |
| KS Gills Properties Ltd | Hospitality | 2021 |
| Kurt Muller International Trade Mark Limited | Professional & scientific | 2005 |
| Kurt Muller Limited | Professional & scientific | 2005 |
| L D F Flooring Contractors Limited | Construction | 2006 |
| L. Whitney Limited | Professional & scientific | 2024 |
| Laminform Limited | Manufacturing | 2005 |
| Landmar Flooring Ltd | Construction | 2006 |
| Lane Plastics Limited | Manufacturing | 1983 |
| Lantech Computers Limited | Information & communication | 1998 |
| Launder & Press (Gosforth) Ltd | Other services | 2025 |
| Laura Bartram Domestic Agency Ltd | Households | 2007 |
| LCR (South Gosforth) Management Company Limited | Households | 1998 |
| LD Property Management Limited | Real estate | 2003 |
| Ld:Northeast | Health & social care | 1996 |
| LEA Widdowfield Roofing & Cladding Limited | Construction | 2007 |
| Leaf IT at Home Limited | Extraterritorial | 2005 |
| Letpost Limited | | 1982 |
| Lexus Enterprises (UK) Limited | Professional & scientific | 2005 |
| Lincoln Haulage Ltd | Transport & logistics | 1998 |
| Lindisfarne Seafoods Limited | Wholesale & retail | 2002 |
| Linkrally Limited | Wholesale & retail | 1993 |
| LKB Developments Ltd | Construction | 2001 |
| Loleo Ltd | Financial services | 2023 |
| Lotus Industries Limited | Wholesale & retail | 2001 |
| Lyndon Systems Ltd | Manufacturing | 2002 |
| M & H Window Manufacturers Ltd | Construction | 1999 |
| M Dobson Double Glazing Limited | Construction | 2003 |
| M J Phoenix & SON Limited | Construction | 1999 |
| M P Electrics Limited | Construction | 2002 |
| M. Millet Electrical Services Limited | Construction | 1999 |
| MAB (GB) Ltd | Financial services | 2006 |
| Machining Techniques Ltd | Manufacturing | 2004 |
| Mackendon Terrace Collingwood Park Limited | Households | 1994 |
| MAK Ventures Limited | Wholesale & retail | 2006 |
| Manor Property Management (North East) Limited | Real estate | 2007 |
| Marchbanks (North East) Properties Limited | Hospitality | 1984 |
| Marlborough House Maintenance (Monkseaton) Limited | Households | 1986 |
| Marshall Painting Contractors Ltd | Construction | 2001 |
| Maskerade Design Limited | Manufacturing | 2007 |
| Mastercraft Enterprises Limited | Professional & scientific | 2003 |
| Mavray Engineering Limited | Professional & scientific | 2004 |
| Maws Pies Limited | Manufacturing | 1993 |
| MAX Signal Limited | Wholesale & retail | 2013 |
| Maximum Control Consultancy Ltd | Information & communication | 2005 |
| MB Consulting (North-East) Ltd | Health & social care | 2004 |
| MCR Engineering Limited | Other services | 2006 |
| MEC Electrical Contractors Limited | Construction | 1966 |
| Medical Enterprises International Limited | Real estate | 2003 |
| Medicare Enterprises Limited | Administrative & support | 2011 |
| Meldon Estates Limited | Real estate | 2000 |
| Metro Security Services (North East) Limited | Administrative & support | 1996 |
| Michael Ward Design Limited | Information & communication | 2002 |
| Miley's Home Improvements Ltd | Construction | 2024 |
| Mill DAM Guest House Limited | Hospitality | 2006 |
| Mincoffs Solicitors LLP | | 2004 |
| Missionbuild Limited | Real estate | 1994 |
| Modern Manufacturing and Trading Ltd | Extraterritorial | 1999 |
| Moguntia Food Ingredients UK Limited | Manufacturing | 1989 |
| Monkseaton Carpet Centre Ltd | Wholesale & retail | 2003 |
| Morevia Estates Limited | Professional & scientific | 2008 |
| Mother Nature (UK) Ltd | Administrative & support | 2002 |