Appointed Professor of Philosophy at Oslo University at the age of 27, a post he held for most of his life. He was also a noted mountaineer.

Not just an academic philosopher he also took practical action. He was inspired by Rachel Carson's book 'Silent Spring (1962) and in 1970 with a number of other activists he chained himself to rocks at the site of a proposed dam. In 1988 he was the founding chairman of Greenpeace Norway and in 2005 stood as a Norwegian Green Party candidate in the General Election in Oslo.

Deep Ecology was attacked by Murray Bookchin,the social ecologist, as a white male academic concern with elements of occultism and paganism and verging on eco-fascism.  On the other hand the Earth First! group used his ideas to justify violent green luddism and programmes of population control which appalled him.

Næss steered a middle course between these competing claims.

He was a visiting teacher at Schumacher College in the UK