| Matformidleren AS | Hospitality | 2026 |
| Mathiesen Invest AS | Financial services | 2010 |
| Mathuset Skippergata AS | Wholesale & retail | 2016 |
| Mathuset Skjelsvik AS | Wholesale & retail | 2012 |
| Matrial AS | Professional & scientific | 2024 |
| Matuva AS | Manufacturing | 2021 |
| Maxbo Tekniske Tjenester AS | Professional & scientific | 2019 |
| MBT Personalrespons AS | Construction | 2017 |
| Meat Shop AS | Wholesale & retail | 2025 |
| Mebto AS | Manufacturing | 2014 |
| Med Byggmester AS | Professional & scientific | 2024 |
| Medalto AS | Health & social care | 2019 |
| Medd Eiendom AS | Real estate | 2016 |
| Mediasparx Ltd Nuf | Information & communication | 2005 |
| Medisinkompaniet AS | Real estate | 2020 |
| Meglerhuset Telemark AS | Real estate | 2020 |
| Mei & Moy AS | Other services | 2021 |
| Meierigaarden B2 AS | Real estate | 2018 |
| Meierigaarden B3 AS | Real estate | 2018 |
| Meierigaarden B5 AS | Real estate | 2024 |
| Meierigården Porsgrunn AS | Real estate | 2025 |
| Mekano AS | Manufacturing | 2024 |
| Mel Porsgrunn 1 AS | Real estate | 2022 |
| Mel Porsgrunn 12 AS | Real estate | 2022 |
| Mel Porsgrunn 13 AS | Real estate | 2022 |
| Mel Porsgrunn 15 AS | Real estate | 2022 |
| Mel Porsgrunn 17 AS | Real estate | 2022 |
| Mel Porsgrunn 2 AS | Real estate | 2022 |
| Mel Porsgrunn 23 AS | Real estate | 2022 |
| Mel Porsgrunn 5 AS | Real estate | 2022 |
| Melbo AS | Wholesale & retail | 2024 |
| Meldalsvei 16 AS | Real estate | 2019 |
| Melfald Invest AS | Wholesale & retail | 2015 |
| Melkeveien 2 AS | Education | 2012 |
| Melkeveien Utvikling AS | Real estate | 2007 |
| Menstad Næringspark AS | Real estate | 2016 |
| Menstad Utbygging AS | Real estate | 2020 |
| Mer Utleie AS | Real estate | 2021 |
| Mere Holding AS | | 2025 |
| Merze AS | Hospitality | 2025 |
| Mester Bygg Øst AS | Real estate | 2016 |
| Mestring Consulting AS | Professional & scientific | 2025 |
| Mestring Holding AS | Financial services | 2017 |
| Metacom AS | Professional & scientific | 1986 |
| MG Bygg Og Eiendom AS | Real estate | 2021 |
| MGM Construction Da | Construction | 2011 |
| Mic VV6B AS | Financial services | 2013 |
| Michel Seylmagers Hus AS | Hospitality | 2024 |
| Michelli Holding AS | | 2022 |
| Microdac Nuf | Professional & scientific | 2012 |
| Midtbøen Dekk Og Service AS | Other services | 2015 |
| Midtech AS | Wholesale & retail | 2017 |
| Midtgaard AS | Real estate | 2021 |
| Miljø Eiendom AS | Real estate | 1997 |
| Miljø Holding AS | | 2005 |
| Miljøpark Grenland AS | Real estate | 1990 |
| Milo-Holding AS | Real estate | 2016 |
| Milton Sykkelshop AS | Wholesale & retail | 2018 |
| Min Barnehage Eiendom AS | Education | 2006 |
| Min Barnehage, Øyekast AS | Education | 2017 |
| Mindspark AS | | 2022 |
| Mitt Emperium AS | Real estate | 2026 |
| Mjølner Bygg & Rehab AS | Construction | 2023 |
| Mjølner Eiendom Ans | Real estate | 2005 |
| MK Eiendom AS | Transport & logistics | 2011 |
| MMB Eiendom AS | Real estate | 2022 |
| Mobiedge Group AS | Real estate | 2006 |
| Mobil Sauna AS | Administrative & support | 2016 |
| Mocadent AS | Real estate | 1998 |
| Mocktail AS | Hospitality | 2021 |
| Modell Og Trafikk AS | Transport & logistics | 2007 |
| Modern Møbeltapetsering & Møbelservice AS | Other services | 2015 |
| Moderne Betongteknologi Da | Construction | 1997 |
| Modul Holding AS | Manufacturing | 2019 |
| Modulbryggen AS | Professional & scientific | 2018 |
| Moen 10 AS | Real estate | 2005 |
| Moen 16 AS | Real estate | 2021 |
| Moen 18 AS | Real estate | 2022 |
| Moen 7 AS | Real estate | 2021 |
| Moen 9 AS | Real estate | 2023 |
| Moen Industri AS | Construction | 2015 |
| Moen-Consulting AS | Professional & scientific | 2022 |
| Moeneiendom AS | Real estate | 2017 |
| Moenholding AS | Energy | 2017 |
| Moheim BKB3 AS | Real estate | 2023 |
| Moheim Næringseiendom AS | Real estate | 2013 |
| Moheim Næringspark AS | Real estate | 2023 |
| Moheim Næringsselskap AS | Real estate | 2007 |
| Moheim Utvikling AS | Real estate | 2019 |
| Mola Invest AS | Agriculture & fishing | 2001 |
| Moltebello AS | Financial services | 2016 |
| Monteris AS | Construction | 2024 |
| Moonage AS | Professional & scientific | 2018 |
| Moratel Eiendomsutvikling AS | Real estate | 2012 |
| Mormor's Stue Bakeri & Spiseri Ans | Wholesale & retail | 1996 |
| Mormor's Stue Da | Hospitality | 1997 |
| Morten Gjeruldsen Holding AS | Wholesale & retail | 2005 |
| Morten Heian Holding AS | | 2021 |
| Morten Johansen Transport AS | Transport & logistics | 2005 |
| Motala AS | Health & social care | 2013 |