Moving to the Italian Front in July 1915 Josef's corps saw action in successive Isonzo battles until, after the Ninth Battle of the Isonzo fought from 1-4 November 1916, he was handed promotion as commander of Austro-Hungarian forces tasked with the Romanian campaign.

With his professional career determinedly in the ascendant Josef suffered a grave setback when, in January 1918, he came out as the sole senior commander to recommend to the Royal Council that separate Austrian and Hungarian armies be instituted. His influence was greatly diminished following this public stand.

His final senior position of the war brought him command in the Trentino sector, replacing former Chief of Staff Conrad. The failure of the Piave River offensive convinced Josef that defeat was imminent and consequently he recommended an immediate peace.

Josef was appointed Field Marshal on 24 October 1918, while the Italian Army was successfully storming his lines at Vittorio Veneto.

With war over Josef led a royalist counter-revolution aimed at overthrowing Bela Kun's communist regime in Budapest. For a brief period he was himself regent but was rapidly replaced by Admiral Horthy in September 1919 upon the insistence of the Allies.

He thereafter took up a position as a Hungarian parliamentarian, eventually ascending to the Upper Chamber where he became a vocal supporter for the notorious Arrow Cross fascist movement.

With the Red Army's entrance into Budapest Josef fled to Austria. He died on 6 July 1962 at the age of 89.