| Magasinet Bunad AS | Information & communication | 2005 |
| Magic Wine AS | Wholesale & retail | 2021 |
| Magna Carta AS | Information & communication | 2016 |
| Magneten Invest AS | Construction | 2019 |
| Magnor Sletten AS | Financial services | 2017 |
| Magnus Velkom AS | Wholesale & retail | 2012 |
| Maho Holding AS | Administrative & support | 2010 |
| Maihaugen Garasjelag SA | Transport & logistics | 1995 |
| Maison Didier AS | | 2026 |
| Majorbygg AS | Real estate | 1958 |
| Malerbua AS | Construction | 2000 |
| Malermester Bjørn Åge Hauen AS | Construction | 2005 |
| Malermester F.A.G AS | Construction | 2012 |
| Malermester Kjellsen & Tufte AS | Construction | 2000 |
| Malermester Morten B - Fredriksen AS | Construction | 2023 |
| Malermester Runar Danielsen AS | Construction | 2005 |
| Malermester Staahlen AS | Construction | 2009 |
| Malmanger Holding AS | | 2020 |
| Malno Holding AS | | 2026 |
| Mammakorak Forlag AS | Arts & recreation | 2023 |
| Manly Holding AS | | 2025 |
| Marbels AS | Wholesale & retail | 2023 |
| Marcus Holding AS | Construction | 2025 |
| Mardes AS | Arts & recreation | 2018 |
| Margit Åkre Reite AS | Health & social care | 2022 |
| Maria Mat AS | Wholesale & retail | 2023 |
| Mariette Da | Wholesale & retail | 1990 |
| Maritime Support AS | Wholesale & retail | 1991 |
| Markedskonsulentene Da | Professional & scientific | 2005 |
| Marker Holding AS | | 2014 |
| Markisebedriften Skien AS | Wholesale & retail | 2022 |
| Marte AS | Real estate | 2015 |
| Martin Nordraaks AS | Financial services | 2005 |
| Marumen AS | Manufacturing | 2016 |
| Mase Strømaggregater AS | Wholesale & retail | 1989 |
| Maskin Entreprenør Roger Nærum AS | Construction | 2006 |
| Maskineriet AS | Administrative & support | 2013 |
| Maskineriet Eiendom AS | Real estate | 2014 |
| Maskineriet Holding AS | Administrative & support | 2013 |
| Maskintjenester AS | Administrative & support | 2011 |
| Master P AS | Wholesale & retail | 2019 |
| Matchbiler AS | Wholesale & retail | 2025 |
| Matek-Samson Regulering AS | Wholesale & retail | 1989 |
| Mathias Berg Holding AS | Professional & scientific | 2018 |
| Mathuset Falkum AS | Wholesale & retail | 2012 |
| Mathuset Frogner AS | Wholesale & retail | 2013 |
| Mathuset Hesselbergsgate AS | Wholesale & retail | 2021 |
| Mathuset Kjørbekk AS | Wholesale & retail | 2011 |
| Mathuset Myren AS | Wholesale & retail | 2007 |
| Mathuset Skien AS | Manufacturing | 2008 |
| Matrise AS | Real estate | 2019 |
| Max Bolig AS | Real estate | 2011 |
| Max G AS | Agriculture & fishing | 2023 |
| Max Utleie AS | Administrative & support | 2001 |
| Maxeta AS | Manufacturing | 1992 |
| Maxhun Eiendom AS | Real estate | 2020 |
| Maxilla Protetikk AS | Manufacturing | 2001 |
| Maxprint AS | Manufacturing | 2003 |
| May Iren Lerbrekk Holding AS | Financial services | 2005 |
| Maykel Entreprenør Service AS | Construction | 2016 |
| Mbmd Invest AS | Real estate | 2025 |
| MC All Eiendom AS | Real estate | 2012 |
| MC All Holding AS | Real estate | 2001 |
| Mcneill Holding AS | | 2026 |
| Meaksmoen Holding AS | Wholesale & retail | 2008 |
| Meca Invest AS | | 2015 |
| Mediaeffekt AS | Professional & scientific | 2012 |
| Medigren AS | | 1993 |
| Medina AS | Hospitality | 2024 |
| Medvind Consulting AS | Professional & scientific | 2022 |
| Meensborg Eiendom AS | Real estate | 2015 |
| Meet AS | Information & communication | 2010 |
| Megaflis Bamble AS | Wholesale & retail | 2022 |
| Meierikvartalet Skien AS | Real estate | 2017 |
| Meivcore Norway Academy AS | Education | 2020 |
| Meivcore Norway AS | Manufacturing | 2011 |
| Meivcore Norway Holding AS | Real estate | 2020 |
| Mekanisk Service Skien AS | Manufacturing | 2026 |
| Meland Eiendom Og Invest AS | Professional & scientific | 2006 |
| Meland Eiendomsmegling AS | Real estate | 2012 |
| Melanders Invest AS | Financial services | 2015 |
| Melby Trening AS | Arts & recreation | 2025 |
| Mele Holding AS | Wholesale & retail | 2024 |
| Melkeveien 11 AS | Real estate | 1997 |
| Melkeveien 13 AS | Real estate | 2008 |
| Mellie Studio AS | Wholesale & retail | 2025 |
| Mellom Mat Og Vin AS | Hospitality | 2026 |
| Meltvedt Gård AS | Health & social care | 2013 |
| Melum Barnehage SA | Education | 1977 |
| Melum Invest AS | Mining & quarrying | 2022 |
| Melum Maskin AS | Construction | 2014 |
| Melum Maskinutleie AS | Mining & quarrying | 2022 |
| Melum Montasje AS | Construction | 2016 |
| Melumvegen 18 AS | Real estate | 2020 |
| Menstad Bolig AS | Construction | 2013 |
| Menstad Mat AS | Wholesale & retail | 2023 |
| Mep Da | Information & communication | 2000 |
| Merci AS | Hospitality | 2024 |
| Mercury Invest AS | Real estate | 2021 |
| Merethe Holding AS | Hospitality | 2005 |