Gustav was 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.
Gustav studied philosophy at the University of Tübingen.
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. 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." Gustav and the other hostages were taken to the cellar of the Luitpold Gymnasium, which had served as a Red Army post since mid-April. The seven Thule Society members, including Gustav, and three Freikorps soldiers were killed on 30 April as a reprisal for reports of the killing of Red soldiers by Whites at Starnberg.
Gustav and his fellow hostages were lined up against a wall and executed by a firing squad.
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. Gustav was the most notable of the four titled members killed in the incident, due to his family"s extensive ties with several of Europe"s royal houses.
Bavarian nuncio Eugenio Pacelli (the later Pope Pius XII) referred to the fights and the murder of the hostages in an article in the newspaper "Bayerischer Kurier" (founded in 1856) on October 1, 1919: "The Nunciature itself was riddled with bullets during the fights between communists and republican government troops. Armed spartacists entered here with force, and when I protested against the violation of international law I was threatened with a gun.
I know in what gruesome manner the hostages were murdered." Titles and styles 22 August 1888 – 30 April 1919: His Serene Highness Prince Gustav of Thurn and Taxis Honours.
Thule Society]
As a member of the Thule Society, Gustav was killed by the Bavarian Soviet Republic (German: Bayerische Räterepublik) government during the of 1918-1919.
