Despite his failure to finish high school, Ossietzky succeeded in embarking on a career in journalism, with the topics of his articles ranging from theatre criticism to feminism and the problems of early motorization. He later said that his opposition to German militarism during the final years of the Hohenzollern empire under Wilhelm II led him, as early as 1913, to become a pacifist. During the years of the Weimar Republic (1918 – 1933), his political commentaries gained him a reputation as a fervent supporter of democracy and a pluralistic society. Also, he became secretary of the Deutsche Friedensgesellschaft (German Peace Society).
It has been claimed that Ossietzky was blind to the dangers of Nazism, which is only true up to a point. He had been a constant warning voice for many years when, in January 1933, Adolf Hitler was appointed Reichs Chancellor and the Nazi dictatorship began. However, Ossietzky was one of a very small group of public figures who continued to speak out against the Nazi party. Accordingly, on 27 February 1933, he was arrested, never to be released again. Wilhelm von Sternburg, one of Ossietzky´s biographers, surmises that if he had had a few more days left, he would surely have joined the vast majority of writers who fled the country. In short, Ossietzky had underestimated the speed with which the Nazis would go about ridding the country of unwanted political opponents.
Ossietzky´s rise to fame set in in 1936 when, already suffering from a serious illness which was not being treated, he was awarded the 1935 Nobel Peace Prize. The Nazis had been unable to prevent this, but they now refused to release him so that he could have travelled to Oslo. In a remarkable act of civil disobedience, Ossietzky issued a note from the hospital where he was being kept prisoner by the Gestapo saying that he disagreed with the authorities who had stated that by accepting the prize he would cast himself outside the deutsche Volksgemeinschaft (community of German people):