He was the founding CEO of ClientEarth, a global non-profit environmental law organisation before moving into the non-executive role of President and Founder.

[7] Now with offices in London, Brussels, Warsaw, Berlin, New York and Beijing, and operating globally, it uses advocacy, litigation and research to address the greatest challenges of our time - including biodiversity loss, climate change, and toxic chemicals.

[9] In 2011, ClientEarth's action[10] in the High Court forced the UK government to admit that it was breaching legal limits for air pollution.

Thornton calls the Common Fisheries Policy 'the worst law in the world'[12] and is working with the Fish Fight campaign of TV chef Hugh Fearnley-Whittingstall to make it workable.

Thornton appeared on stage with Brian Eno at the Luminous Festival, Sydney Opera House, in 2009 to discuss the environment.

His latest book, Client Earth is described by Nature as "a tantalizing glimpse of how a variety of strategies can converge to create a global environmental enforcement effort."

[3] He did a retreat with the Indian teacher Mother Meera in Germany for 14 months, after which he started Positive Futures, an organization to teach meditation to environmental activists.

[25] For some years he was executive director of the Heffter Research Institute, which worked on the medical application of hallucinogens [26] among other neuroscience developments.

[28] Attraction to study with the Japanese Zen Master Taizan Maezumi Roshi, was a reason why Thornton moved to San Francisco in 2009.