Born in Germany in 1911,[citation needed] in 1934 he moved to Kibbutz Ayelet HaShahar and then Ein HaShofet in Palestine. He fought with the International Brigades during the Spanish Civil War. Avidan is also known for his activities in the Palmach in World War II. He led the "German Unit" of the Palmach, which was responsible for conducting guerilla operations against the Axis powers. In 1945 he commanded the Saison operation against the Irgun and Stern Gang.