Somerhalder, who campaigns tirelessly on topics such as habitat, energy and animals through his IS Foundation, is up against sustainable fashion supporter Livia Firth and Asian star eco-activist Nadya Hutagalung for the title.
Best known as smouldering vampire Damon Salvatore in the hit US show and for his previous starring role as Boone Carlyle in long-running TV drama 'Lost', Somerhalder was also recently honoured at the Environmental Media Awards in LA with the Futures Award.
As well as setting up and running his own foundation, he is also an Ambassador for the United Nations Environment Programme (UNEP), where his work has included a video call-to-arms for people to participate in environmental activity.
Talking about his environmental work, he recently said: "I don’t know how to do anything else other than be an actor. If I wasn’t in this, I would be in alternative energy and conservation."
The aim of the International Green Awards is to raise the bar around the 'cult of celebrity' and the award hopes to put the spotlight on progressive individuals who harness the power of the media and challenge conventional thinking on the climate agenda.
The winner, who will take the title from last year's greenest celeb - international supermodel Gisele Bündchen - will be announced on Tuesday 20 November at Battersea Power Station, London.
Who do you think is the greenest celebrity?