Upon returning to France, Fernex founded a chapter of the third world relief group,
Terre des hommes. She worked to preserve historic homes and assisted with the "squatting" movement to successfully protest a proposed lead factory on the Rhine River and a nearby chemical plant. She also joined activists in opposing nuclear power plants, including one planned in Wyhl in southwestern Germany, where she camped in a protest community near the site. In 1977, Fernex was elected to her town council and remained active on it for 24 years. In 1979, she led the Europe-Ecologie political movement for the environmental group's first European elections, which obtained 4.39 percent for a total of 888,134 votes in France. That same year, she founded the women-led peace organization, Femmes pour la Paix, which she headed until 1996. In 1983, she participated in the
Fast for Life movement, fasting 38 days in Paris for
nuclear disarmament. The following year, she co-founded the
Green Party with
Antoine Waechter. She was the lead organizer in Europe of the
Walk of the People – A Pilgrimage for Life, a transcontinental peace walk from the United States to Russia that covered 7,000 miles in 1984 and 1985. ==Chernobyl, European Parliament, later years==