He was the son of Captain Joseph Zacharias Vorster and Countess Anna Maria Rosa Berni.

He was penalized and was moved in September 1788 as suboeconomus (vice governor) to Ebringen, a St Gall domain under Austrian suzerainty south of Freiburg im Breisgau.

Vorster moved to Neu-Ravensburg, an exclave north of Lake Constance, and formally raised a protest against his subjects' action on 3 March 1798.

After the invasion of France, Vorster tried in vain to remove the Abbey from Switzerland with a proclamation on 9 June 1798, so as to rejoin the Holy Roman Empire.

Instead, Vorster received St. Gallen from the bishop of Basel, Franz Xaver von Neveu, on 4 November 1804 in Offenburg.

In 1814–1815 Vorster personally asked the Congress of Vienna to recover his rule, but could only obtain a pension of 6000 florins, while the canton retained control of St. Gallen.

Vorster unsuccessfully attempted, with the support of the pope, to get the affiliation of at least one Diocese of St. Gallen before the Federal Council at Tagsatzung on 16 July 1816.