She participated in the Ligue Internationale pour l’Éducation Rationnelle de l’enfance (International League for the Rational Education of Childhood), founded by Francisco Ferrer in 1908.
[3] Beginning on August 21, 1912, and every week thereafter, in the antimilitarist newspaper La Guerre sociale she wrote a column for women titled "Notre coin" (Our corner).
[3] Clar wrote articles for the feminist newspaper La Voix des femmes (founded in 1917 by Colette Reynaud and Louise Bodin) when it was relaunched in October 1919.
In 1924, Madeleine Vernet, Éliane Larivière, Fanny Clar and Marceline Hecquet co-signed an "Open Letter to the Governments" ("Lettre ouverte aux gouvernements") calling for a complete and general amnesty, a rapid evacuation of the Ruhr and the re-establishment of political and commercial relations with Germany.
[3] Jean Vigo hired Clar for the role of Juliette's mother (uncredited) in the film L'Atalante in 1934,[3] and she went on to promote the movie.