He travelled extensively, including journeys to Asia Minor, Malta, and Ephesus, and, in 1615, to Lapland.

After the bloodless Cherry War later that year, he had to leave the League under the terms of the Peace of Tübingen.

This led to a dispute with the Government, the Estates, and his co-regent (Barbara Sophie of Brandenburg, the mother of Eberhard III).

After the Battle of Nördlingen, the whole ducal family, including Julius Frederick, fled to Strasbourg, where he died the following year.

On 24 November 1617, he was engaged to Princess Anna Sabine von Schleswig-Holstein-Sonderburg (7 March 1593 – 18 July 1659), daughter of John II, Duke of Schleswig-Holstein-Sonderburg and his second wife, Princess Agnes Hedwig of Anhalt.