Julius Frederick was the third son of the Duke Frederick I of Württemberg and his wife Sibylla of Anhalt. He grew up with his parents and siblings in Montbéliard. After his father took up government of Württemberg in 1593, Julius Frederick lived in Stuttgart. He participated in military operations in the Alsace and in the War of the Jülich Succession. He travelled extensively, including journeys to Asia Minor, Malta, and Ephesus, and, in 1615, to Lapland.
