Stojsavljevic graduated from the Maria Theresa Military Academy in 1908. After serving in the infantry, he transferred to the Army Air Service in 1913 and was posted to Flik 13 as a reconnaissance pilot in November 1914. On 16 February 1915, he and his observer were captured by the Russians when their two-seater was forced down by a snow storm. Escaping six days later, the two men evaded the enemy for months until they reached the safety of their own lines in June 1915. Stojsavljevic was posted to Flik 17 later that summer and in September 1915 he joined Flik 16 where he scored his first four victories in 1916. In February 1917, he was posted to Flik 34 for two months. With this unit he learned to fly the Hansa-Brandenburg D.I, scored his fifth victory and injured his knee in a crash. In May 1917, Stojsavljevic served briefly with Jasta 6 at Cambrai before rejoining Flik 16. Having scored five more victories in 1917, he was badly wounded in a dogfight on 12 January 1918. After a lengthy recovery, he returned to duty in October 1918 and was appointed commander of the Officers Flight School at Wiener-Neustadt.