Andreas Hinterstoisser was born on 3 October 1914 in Bad Reichenhall, Bavaria, Germany, where he was raised. He worked in a bank before joining the German Wehrmacht as a professional soldier in 1935. Together with his childhood friend Toni Kurz, he made numerous first ascents of peaks in the Berchtesgaden Alps, including some of the most difficult climbs of that time. The two young men climbed the southwest wall of the Berchtesgadener Hochthron in 1934, and the south wall of the straight pillar in 1936. They also made first ascents in the Reiter Alpe on the German-Austrian border, and of the direct southern route up the Watzmannkinder in the Watzmann in 1935.