| Logiq AS | Information & communication | 1999 |
| Loke Consult AS | Professional & scientific | 2017 |
| Lokstallen AS | Real estate | 2011 |
| Lorensteen Holding AS | Real estate | 2025 |
| Lori-Frisør AS | Other services | 2021 |
| Lotus Blomster Halden AS | Wholesale & retail | 2023 |
| Loxia Invest AS | | 2022 |
| Loxy AS | Manufacturing | 1979 |
| Loyd Holding AS | | 2026 |
| Lro Holding AS | | 2024 |
| Lumi by Therese AS | Other services | 2018 |
| Lundestad Landbruk AS | Real estate | 2006 |
| Lundinnovation AS | Professional & scientific | 2010 |
| Lundsholt AS | Real estate | 2009 |
| Luno Invest AS | Real estate | 2025 |
| LXS Invest AS | Wholesale & retail | 2021 |
| Lydmuren AS | Arts & recreation | 2023 |
| Lykkebo AS | Real estate | 2023 |
| Lykkebo Design AS | Professional & scientific | 2024 |
| Lysløypa Barnehage AS | Education | 1995 |
| Løchen Eiendom AS | Wholesale & retail | 1998 |
| Lødeng Eiendom AS | Real estate | 2008 |
| Lødeng Invest AS | Real estate | 2014 |
| Løve Eiendom AS | Real estate | 2018 |
| Løwengreens Autospa AS | Other services | 2021 |
| M & M Eiendom AS | | 2001 |
| M Hannestad AS | Transport & logistics | 1983 |
| M Langvik Holding AS | | 2022 |
| M M Two AS | Professional & scientific | 2017 |
| M&M Invest AS | Real estate | 2006 |
| M&M Optikk AS | Wholesale & retail | 2021 |
| M&W Holding AS | | 2026 |
| M-T Holding AS | | 2021 |
| Macman AS | Professional & scientific | 2015 |
| Maersk Accountancy & Vat Services Norway AS | Professional & scientific | 1997 |
| Maersk Logistics & Services Norway AS | Transport & logistics | 1991 |
| Magjon AS | Real estate | 1987 |
| Magne Gundersen Kran Og Transport AS | Transport & logistics | 2013 |
| Magnusson Landbruk Da | Agriculture & fishing | 2022 |
| Mahe Invest AS | Financial services | 2005 |
| Make Eiendom AS | | 2013 |
| Makebe AS | Wholesale & retail | 2018 |
| Maky AS | Real estate | 2009 |
| Malcolm AS | Arts & recreation | 2026 |
| Maler Bent Rørmyr AS | Construction | 2014 |
| Malerfirma Magne Ekstrøm AS | Construction | 2025 |
| Malerfirma Sandmo AS | Construction | 2025 |
| Malermester Odd Jansen & Sønn AS | Construction | 1998 |
| Mali Holding AS | | 2021 |
| Malima Invest AS | Financial services | 2023 |
| Mamola AS | Wholesale & retail | 2019 |
| Manforte Ans | Professional & scientific | 2005 |
| Marcin Invest AS | Real estate | 2015 |
| Marcopolo Pizza AS | Hospitality | 2020 |
| Marcus Thranes Gate 30 AS | Real estate | 2014 |
| Marina Strand SA | Water & waste | 2022 |
| Marit Henriksen AS | Wholesale & retail | 2005 |
| Marius Lauritzen AS | Professional & scientific | 2026 |
| Marker Frakt Og Utleieservice AS | Transport & logistics | 2021 |
| Markveien Holding AS | | 2005 |
| Martin Andre Olsen AS | | 2019 |
| Martin Glomsrød Eiendom AS | Real estate | 2020 |
| Mastermind Regnskapstjenester AS | Professional & scientific | 2006 |
| Mat Og Trebåtfestivalen AS | Hospitality | 2011 |
| Mathisen Legetjenester AS | Health & social care | 2023 |
| Matias Holding AS | Other services | 2022 |
| Max Caravan AS | Wholesale & retail | 2017 |
| Max Scandinavia AS | Wholesale & retail | 2012 |
| Maxmill Group Holding AS | | 2005 |
| MB Entreprenør AS | Construction | 2018 |
| Mbe Gruppen AS | Real estate | 2020 |
| Mbe Utvikling AS | Real estate | 2016 |
| Medilens Norge AS | Wholesale & retail | 2018 |
| Medy AS | Health & social care | 2021 |
| Medy Solutions AS | Health & social care | 2024 |
| Mek & Sveis AS | Construction | 2023 |
| Mekanisk Service Halden AS | Manufacturing | 1993 |
| Mela Holding AS | | 2026 |
| Melvin Langvik AS | Information & communication | 2026 |
| MESTER1 Hus AS | | 2023 |
| Mesterbad Halden AS | Construction | 2025 |
| Mesterbygg Halden AS | Construction | 1993 |
| Mettes Multikonsept AS | Wholesale & retail | 2014 |
| Meya AS | Professional & scientific | 2017 |
| MG Byggetjenester AS | Construction | 2025 |
| Michael Wahlstrøm Bygg Og Vedlikehold AS | Construction | 2016 |
| Midpoint Solutions AS | Wholesale & retail | 2022 |
| Miett Holding AS | | 2025 |
| Miku AS | Wholesale & retail | 2025 |
| Milmik AS | Professional & scientific | 2018 |
| Mimir Drivkraft AS | Professional & scientific | 2026 |
| Min Lilla Salong Skandinavia AS | Other services | 2021 |
| Minicloud AS | Wholesale & retail | 2025 |
| Mira Holding AS | | 2025 |
| Mitt Hotell AS | Hospitality | 2018 |
| Mjøber Da | Agriculture & fishing | 2000 |
| Mjølnerød & Mjølnerød Eiendom Da | Real estate | 2001 |
| Mjølnerød Dagligvare AS | Wholesale & retail | 2020 |
| Mjølnerød Holding AS | Health & social care | 2024 |
| Mjølnerød Høy Og Halm AS | Agriculture & fishing | 2018 |