During his term of office, Stüssi attempted to extend the rule and influence of his city. In 1436, Count Friedrich VII of Toggenburg died, leaving neither heir nor will. The canton of Zürich, led by Stüssi, claimed the Toggenburg lands; the cantons of Schwyz and Glarus made counter-claims, backed by the other cantons. Stüssi allied himself in 1442 with Frederick III, Holy Roman Emperor against the Old Swiss Confederacy.
He died at the Battle of St. Jakob an der Sihl, defending the bridge over the Sihl while covering the retreat of the army of Zürich. According to chroniclers, he was killed by a confederate hiding below the bridge. Another version of the story has Stüssi stopping in the middle of the bridge, brandishing his broad battle-axe and shouting, "Halt, citizens, halt!" To this a man of Zurich cried, "May God's lightning blast thee! All this evil comes from thee alone," and ran him through with his lance.