The eldest son of King Oscar II and Sophie of Nassau, he was created duke of Värmland and from 1872 acted as crown prince. In 1881 he married Victoria, daughter of the grand duke Frederick I of Baden. Succeeding on his father's death (Dec. 8, 1907), he took as his motto “With the people for the Fatherland” and proved a capable constitutional monarch in a period of expanding democracy within his country.

During the Courtyard Crisis in February 1914, Gustav declared his support for demands that Sweden strengthen its defenses. He was accused of overstepping his authority, but, with wide popular support for his actions, he was able to force the resignation of the Liberal government that had decreased military expenditure. He appointed a Conservative government under the leadership of Hjalmar Hammarskjöld (Hammarskjöld, Hjalmar). After World War I, Gustav accepted his position as a constitutional monarch as a consequence of the full emergence of parliamentary government and the franchise reforms in 1917 and 1918.