The younger son of Henry VII, count of Schwarzburg-Blankenburg (died 1323), Günther inherited Blankenburg and Saalfeld in 1330. He served as a diplomat and military commander for Louis IV from 1334 to 1339. After Louis IV's death, the electors of Brandenburg, Saxe-Lauenburg, Frankfurt, and the archbishopric of Mainz, who were partisans of the Wittelsbach house, of which Louis IV had been a member, offered the throne to Edward III, king of England. When Edward declined (1348), they offered it to Günther; he was elected king at Frankfurt on January 30 and crowned on Feb. 6, 1349.

Günther, however, did not have clear title to the throne because the Reichstag (imperial diet), which had been alienated by Louis IV's dynastic policies, had elected Charles of Luxembourg, margrave of Moravia, anti-king on July 11, 1346. Charles IV won over many of Günther's followers and defeated him at Eltville. By the terms of the Treaty of Eltville (May 26, 1349), Günther, who was mortally ill, accepted 20,000 silver marks and amnesty for his supporters in exchange for relinquishing his claim to the German throne.