He founded Der Spiegel in 1946/1947, which became (and still his) the most important investigative weekly magazine in Germany. During the Spiegel scandal in 1961 and 1962, he was arrested and jailed for several months, until Franz Josef Strauß was forced to resign as Minister of the Defense under continuing public protest.
Augstein became a member of the Bundestag in 1972, but gave back his seat already in 1973 to focus on his duties as a journalist. It has been speculated that he considered himself to extert much more influence with his magazine.
A hobby historian, Augstein published several successful books, among them Preußens Friedrich und die Deutschen (1981, ISBN 3891901062), Otto von Bismarck (1990, ISBN 3445060126), and, about his lifetime opponent, Überlebensgroß Herr Strauß. Ein Spiegelbild (1983, ISBN 3499330024).
Since Stefan Aust became editor-in-chief of Der Spiegel, Augstein retreated more and more to private life, although he continued to publish commentaries regularly in the magazine almost until his death. For his lifetime achievements for peace, civil liberties and freedom of the press he was honoured with the title "Journalist of the century" in 2000 by 101 German journalists.
Augstein married five times, the last time in 2000. He died on November 7, 2002 from pneumonia and was buried on the island of Sylt.