Karl Otto Adolf Arndt (March 12, 1904 – February 13, 1974) was a German politician and a member of the SPD. He was born in Königsberg and died in Kassel.
Born in Königsberg as the son of the Law professor Gustav Adolf Arndt, he moved to Berlin very early with his family. There, he passed his Abitur at the Gymnasium Philippinum Marburg. Then, Arndt studied Law, Economics and Philosophy at the University of Berlin and the University of Marburg. After passing his second examination and promotion in Marburg in 1927, he worked as a lawyer in the famous law firm of Prof. Dr. Max Alsberg. Since 1932, he worked as a judge, but retired in 1933, stating he did not want to join the Nazi Party. Thus, he joined the law firm of Fritz Schönberg in Berlin, helping (among others) Wilhelm Leuschner and Theodor Leipart. After being classified as half Jewish, Arndt was forced to compulsory labour in the Organisation Todt.
In August 1945, Arndt was approved as a lawyer and notary in Marburg. In November 1945, he became Ministerialrat (Head of Division) of Criminal law at the Ministry of Justice of Hesse.