Popović was drafted to fight for Austria-Hungary in Summer of 1914, he was sent to fight on Serbian front. In Autumn of 1914, he was heavily wounded during a battle and he was sent back to Hungary to recover. In 1916, he became an officer of engineer corps and was sent to Romanian front, where he worked on re-construction of bridges and restorations of army communications. He was later transferred to the Italian front where he remained until the end of the war.