He commanded the Hungarian I Corps during the Invasion of Yugoslavia.
In 1941, he was deputy chief of General Staff (May–October) and deputy commander in chief of the Army (November).
Between 1 November 1941 and 3 December 1942, he commanded the 3rd Army, which occupied a part of Yugoslavia.
After he graduated in Defense Force Academy of Pécs, he served in 1906 at 19º Regiment of Infantry of Army in Pécs. At the First World War, during forty months, he fought at the front.
In 1923 he graduated in Military Academy of Budapest. From 15 November 1927 to 1 May 1931, he was assistant of Chief-Commandant of Defense Army. On 1 August 1933 he became chief of 1st Hungarian Brigade. In 1936 he was nominated chief of Department of Ministry of Defense.[4] He also was vice chief of defence Staff since 1 November de 1938, in January of the same year, he was promoted to major-general and on 1 September 1940 to Lieutenant-General.
In March 1940 he became commander of the Hungarian I Corps, with which he participated in the annexation of Northern Transylvania in September 1940 and at the Invasion of Yugoslavia on 5 April 1941. After the occupation of Yugoslavia, he became Deputy Chief General Staff between May and November 1941 and was then appointed commander of the Hungarian Third Army, which occupied the Hungarian sector of Yugoslavia, until December 1942.
He was nominated general secretary on 1 October 1942. On 17 December 1943 he was nominated a Private Royal Counsellor of Royal Council of Miklós Horthy, Regent of Hungary from 1920 to 1944. In March 1944 he was condecorated with the Cross of Hungarian Order of Merit. His son László, after the abdication of Miklós Horthy, whom he supported, went into exile in Portugal and later to Brazil.[5] Zoltán's illegitimate son, Ferenc Vitéz Decleva (1942-2016), became Capitan of Baranya County, colonel of the Hungarian National Guard and a member of Knights of Saint George.[6]
Zoltán Decleva died on 17 July 1950 in Budapest. At 2004, he was graced posthumously with an Order of Vitéz.