| Mamba AS | Arts & recreation | 2006 |
| Management Synergy AS | Education | 2009 |
| Mangor AS | Mining & quarrying | 2021 |
| Manthus AS | | 2015 |
| Maria Eiendom AS | Real estate | 2021 |
| Marin Supply AS | Wholesale & retail | 2020 |
| Marina Frisør AS | Other services | 2017 |
| Maritim Utdanning AS | Education | 2017 |
| Martin Olsen AS | | 2005 |
| Masch Holding AS | | 2026 |
| Maslinica AS | | 2024 |
| Masoma AS | | 2021 |
| Massørklinikken AS | Health & social care | 2015 |
| Masteen AS | Professional & scientific | 2002 |
| Master Online AS | Arts & recreation | 2000 |
| Masterbolig AS | Real estate | 2019 |
| Masterbygg AS | Real estate | 2012 |
| Masterpoint Akupunktur Buvarp AS | Health & social care | 2000 |
| Mat Invest AS | Professional & scientific | 1997 |
| Matidi AS | Wholesale & retail | 2024 |
| Maverick Holding AS | | 2022 |
| Maxxol Norge AS | Wholesale & retail | 2010 |
| Maya Klinikk AS | Other services | 2026 |
| Maytimber AS | Professional & scientific | 2017 |
| MB Bygg & Takst AS | Construction | 2025 |
| MB Henriksen Holding AS | Professional & scientific | 2025 |
| MBG Invest AS | | 2018 |
| MBM AS | Professional & scientific | 2008 |
| Meah Design Da | Professional & scientific | 2020 |
| Mecca Gym Tønsberg AS | Arts & recreation | 2020 |
| Med-Eq AS | Professional & scientific | 2015 |
| Medbuddy AS | Information & communication | 2024 |
| Medex Norge AS | Wholesale & retail | 2019 |
| Medfa-Walta Da | Hospitality | 2025 |
| Medicalis Tønsberg AS | Health & social care | 2017 |
| Medikomp AS | Wholesale & retail | 2016 |
| Medira Regnskap AS | Professional & scientific | 2022 |
| Mega Flis Tønsberg AS | Wholesale & retail | 2003 |
| Megler Holding AS | Real estate | 2005 |
| Megleroppgjøret AS | Real estate | 2008 |
| Mehold AS | | 2023 |
| Meierigata Eiendom AS | Real estate | 2018 |
| Melandsø Invest AS | | 2005 |
| Memo AS | Wholesale & retail | 1998 |
| Memo Forvaltning AS | Real estate | 2006 |
| Memo Næringseiendom AS | Real estate | 2006 |
| Meo Invest AS | | 2021 |
| Merci Textile AS | Manufacturing | 2026 |
| Merkur Kompetanse AS | Professional & scientific | 2008 |
| Messehuset Tønsbergs Turnforening Venner AS | Real estate | 2013 |
| Mester Eiendom Tønsberg AS | Real estate | 1995 |
| Mesterhus Tønsberg AS | Real estate | 1993 |
| Metiri AS | Real estate | 2020 |
| Mettro AS | Real estate | 2005 |
| Meyers Farvehandel AS | Wholesale & retail | 1999 |
| Mgaholding AS | Professional & scientific | 2022 |
| Mgmt Assistants AS | Professional & scientific | 2025 |
| MHB Group AS | Wholesale & retail | 2017 |
| MHC AS | Wholesale & retail | 2005 |
| Mhint Arkitektur AS | Professional & scientific | 2020 |
| MHK Eiendom AS | Real estate | 2025 |
| MHK Holding AS | Construction | 2021 |
| Micasa AS | Real estate | 1993 |
| Micasa Invest AS | Real estate | 1998 |
| Micofresh AS | Professional & scientific | 2025 |
| Middelborg AS | Real estate | 2005 |
| Middelborg Eiendom AS | Real estate | 2006 |
| Middelborg Invest AS | Real estate | 2006 |
| Middelborg Utvikling AS | Real estate | 2011 |
| Midtechnology AS | Professional & scientific | 1998 |
| Midtløkken Legekontor Da | Health & social care | 2006 |
| Mikroliber AS | Information & communication | 2024 |
| Mil Palmeras AS | Real estate | 2019 |
| Mila App AS | Information & communication | 2023 |
| Mila AS | | 2005 |
| Mila Shop AS | Professional & scientific | 2021 |
| Mila Shop Invest AS | Professional & scientific | 2021 |
| Mileveien Eiendom AS | Real estate | 2026 |
| Militarium AS | Real estate | 2015 |
| Mimag Da | Real estate | 2016 |
| Mimazi AS | Professional & scientific | 2019 |
| Mimesis SA | Arts & recreation | 2010 |
| Mindcom AS | Information & communication | 2026 |
| Minipero AS | Real estate | 2022 |
| Minlillehobby AS | Wholesale & retail | 2010 |
| Mirai Eiendom AS | Real estate | 2020 |
| Mirai Utleie AS | Administrative & support | 2005 |
| Mish AS | Real estate | 2019 |
| Misjon AS | Health & social care | 2018 |
| Mispelveien 1 AS | Real estate | 2022 |
| MK Oversettelse AS | Professional & scientific | 2018 |
| MMD Groop AS | Wholesale & retail | 2025 |
| Mo Interiør Tønsberg AS | Wholesale & retail | 2022 |
| Modern Society AS | Wholesale & retail | 2020 |
| Moer Holding AS | Construction | 1996 |
| Moer Installasjon AS | Construction | 1979 |
| Moksha AS | Hospitality | 2023 |
| Monstad Bygg AS | Construction | 2011 |
| Moovment AS | Wholesale & retail | 2021 |
| Morgengry Interiør AS | Wholesale & retail | 2026 |