He resigned from his Parisian dental practice after a few months, leaving for Soissons after being hired by the American Committee for Devastated France.

An ardent promoter of peace, he lectured in France and Germany on the principles of naturism and vegetarianism.

He argued that they contributed to hygienic living and the progress of the "moral and spiritual values of which man is the bearer".

[2] The Trait d'Union activists held a stand at the Paris fair and distributed leaflets supportive of naturism and vegetarianism.

[2] Demarquette acquired land in Choisel, near Chevreuse where they practiced naturist camping and sunbathing.

In 1924, Demarquette organized lecture tours in popular universities and to other temperance and vegetarian societies.

[2] When Demarquette returned to Paris in the 1932 he noted in his memoirs that cooperation amongst the society was in a poor condition as managers had hired other workers to do work whilst they were sunbathing.

With debts to pay the society was reorganized and put back on track with help from Lucien Samson, an administrator.

However, by the late 1930s most of the society's members held interest in naturism and vegetarianism for health and hygienic reasons, not as an ascetic spiritual discipline.

[2] In 1953, Demarquette founded the Association Végétarienne de France, a vegetarian organization in Paris.