He served as Germany's Federal Minister of the Interior from 1974 to 1978 until he resigned after a scandal involving an illegal wiretapping of Klaus Traube.

An avid speed skater in his youth, Maihofer was a member of the German national team at the 1936 Winter Olympics in Garmisch-Partenkirchen.

One of the leaders of thought of social liberalism in Germany, he co-authored the Freiburg theses alongside Karl-Hermann Flach and Walter Scheel in 1971.

In 1974, he succeeded Hans-Dietrich Genscher as Federal Ministry of the Interior, and—during the German Autumn—had to back several restraints of civil liberty.

Suspected contacts were monitored in the hope of gaining information that might lead to the capture of the militants.