[2][3] His father was from Ulm and in 1893, created a powdered milk factory in Wiedemannsdorf, Oberstaufen that was one of three in Germany to produce the recently invented product.

[8] During World War II, Kast was first deployed on garrison duty in France in 1942, then he fought the Soviet Union in 1943 through 1944 during the Battle of Korsun–Cherkassy.

[8][9][10] In 1944 and into 1945, he was deployed to Italy to defend the Gothic Line in the Apennine Mountains and was caught by an American unit near Trento in May 1945.

[8] Kast escaped from custody during a guard change the following month and fled back to Bavaria on foot using ratlines, where he subsequently obtained a false ID indicating he was a member of the International Committee of the Red Cross according to journalist Javier Rebolledo.

[8][9] In Bavaria, Kast met his future wife, born Olga Maria Kreszencia Rist (1924–2015) but generally known in Chile thereafter as Olga Rist Hagspiel, in accordance with Spanish language naming traditions, whereby both parents' surnames are formally and legally carried.

[14] Kast's exact involvement in World War II and under Augusto Pinochet's military dictatorship has been a subject of controversy.

Journalists Javier Rebolledo and Nancy Guzmán distinctly called Michael Kast a Nazi in their 2015 book, titled A la sombra de los cuervos.