The youngest artist to paint the Queen, Dan Llwelyn Hall, has joined campaigners in Euston Square Gardens over the removal of trees for HS2.
The painter began work on a new mural on Friday called the Green Grim Reaper.
Hall and other activists say green spaces are vital in maintaining London's air quality and natural balance.
The piece will be part of a larger collection meant to engage the public with the protests.
An HS2 spokesperson issued a response to Friday's demonstration.
"We are working with London Borough of Camden to ensure that all trees lost during construction are replaced and other open spaces in the local community are enhanced. HS2 will create a 'green corridor' consisting of new woodland, wildlife habitats and new amenity facilities to leave a lasting legacy of high-quality green spaces all along the route."