Förschner was born in the town of Dürrenzimmern (today part of Nördlingen), Bavaria on 4 November 1902, and was raised on a farm owned by his family.

[1] Between April 1934 and December 1936, Förschner attended the SS training camp at Bad Tölz, and became a member of the Nazi Party in 1937.

In September 1943, Förschner was given command over the newly built concentration camp of Mittelbau-Dora, which at this time functioned as a sub-camp of the much larger Buchenwald.

In addition to his position as commandant at Dora, Förschner was also technically the managing director of Mittelwerk GmbH, the front company created by the German government for V-weapons production.

Förschner's reputation in the Nazi party was badly damaged in November 1944, when many of the prisoner functionaries he had appointed were rounded up by the Gestapo and revealed to have been involved in resistance activities inside the camp, most notably the sabotage of V-weapons during the production process.