When Geismar finally retired in January 1923, he became increasingly active in the Zionist movement, assisting the development of Keren Hayesod (Reconstruction Fund), with André Spire. He then became honorary president of the K.K.l (Keren Kayemeth Leisrael or Jewish National Fund)'s Central Commission. His knowledge of Hebrew made him able to read Mandatory Palestine's press. He participated and was a member of the steering committee for , a Zionist advocacy group founded in 1926 by Joseph Paul-Boncour et Justin Godart. His fellow members included Édouard Herriot, Paul Painlevé, Jules Cambon, Aristide Briand, Raymond Poincaré, Alexandre Barthou, and Gaston Doumergue. The society's Secretary-General was Henri Hertz. In 1927, he was elected to the executive committee of the de la Zionist Federation of France.Job 2006, p. 139. He helped found the Franco-Palestinian Centre of Commerce. In 1928, he accepted the presidency of the Éclaireuses et éclaireurs israélites de France (EEIF), saying he was "training the young recruits of the Jewish people."
