Raised in the Šopron and Pozega's Jesuits, but opted for military service. From the 1741. he participated in the Austrian hereditary war with troop volunteers and amnesty brigands known as Trenkova cops, with whom he successfully fought in Silesia, Austria, Bavaria and Bohemia.
Trenk has survived 102 duels. As in war, as in duels was wounded 14 times and twice sentenced to death. He was the son of Colonel, Prussians who out of gratitude you got a good military service of the Empress Maria Theresa, moved to Catholicism. Although he wasn't a Croat origin, the appearance of Baron Franjo Trenk in Croatian history and the history of warfare has left a memorable impression. Under his command, Croats, mostly from the province of Slavonia, were celebrated as great warriors.