[2] Gustav was born in Dresden, Kingdom of Saxony as the fourth child and second son of Prince Franz of Thurn and Taxis and his wife Countess Theresia Grimaud of Orsay.
Through his father, Gustav was a grandson of Maximilian Karl, 6th Prince of Thurn and Taxis and his wife Princess Mathilde Sophie of Oettingen-Oettingen and Oettingen-Spielberg.
[1][3] As White Guard (German: Weisse Garde) forces (a coalition of Prussian and Bavarian troops combined with Freikorps) surrounded Munich, the Communists began to raid nationalist strong points throughout the city.
[3][4] On 26 April 1919, the Red Army (German: Rote Armee) broke into the Thule Society premises and arrested secretary Countess Heila von Westarp, Gustav, and five other members, labelling them as "right-wing spies.
[1][6] Their deaths may have also been a reprisal for an attempt by Thule Society members to infiltrate the Bavarian Soviet Republic's government and stage a coup d'état on 30 April.