His cousin Widukind of Waldeck was Bishop of Osnabrück from 1265 to 1269, and his nephew Conrad II of Sternberg was Archbishop of Magdeburg from 1266 to 1277.
In 1268, Günther became provost in the Dionysius monastery in Enger, and also canon in Magdeburg where his nephew Conrad was archbishop.
Conrad died in 1277 and Günther succeeded him, after a disputed election, in which he defeated Bernard III of Wölpe, the cathedral cellarer.
Around that time, a feud broke out, because Margrave Otto IV of Brandenburg wanted his younger brother Eric elected as Archbishop, and had made an alliance with the Duke of Saxony against Günther.
Günther, supported by a strong force from the City of Magdeburg, defeated Otto in battles at Aken and Frohse (10 January 1278).
His election was confirmed by the ecclesiastical province of Mainz and Emperor Henry VII transferred the regalia of Paderborn to him.