In 1862, during the bombardment of Belgrade by the Ottoman Turks, Lešjanin commanded a section of the defence and was promoted to the rank of captain I class.

At the beginning of the First Serbian–Turkish War in the summer of 1876, Lešjanin (who was promoted to the rank of colonel the previous year) commanded the Timok Army, which aimed to invade the northwestern Ottoman Bulgaria and to raise the Bulgarians in revolt.

His attempt to accomplish this task was thwarted by the Turks; Lešjanin then ceded command to the Imperial Russian Army general Mikhail Chernyayev.

[1] In the Serbo-Bulgarian War in November 1885, General Lešjanin commanded the Timok Army during the unsuccessful siege of Vidin.

[4] After the war, Lešjanin took over the leadership of the General Staff for the third time, in 1886–1888; afterwards, he left the Royal Serbian Army and entered politics.