Karl Steinhardt (1 August 1875, Gyöngyös — 21 January 1963, Vienna) was an Austrian politician and activist who was one of the founders and leaders of the Communist Party of Austria.
He continued his work as a printer throughout Europe and eventually settled in Hamburg where he was later expelled for his political activities.
He went to Vienna in 1913 and became fully committed to political activism until he was expelled from the SDAPÖ for during the First World War for his internationalist stance and anti-war propaganda.
After he managed to get in contact with the International Red Cross he was set free and returned to Vienna.
From 1945 to 1949 he was a member of the Gemeinderat and Landtag of Vienna for the KPÖ and was also elected to the central committee of the party.