During the Austro-Prussian War of 1866, Maroicic served on the Italian front in the South Army commanded by Archduke Albrecht. Maroicic commanded the 7th Army Corps, with which he distinguished himself at Custoza. After the defeat of Benedek and the Northern Army at Königgrätz necessitated the transfer of troops from the Italian front northwards to cover Vienna, Maroicic held the line at the Isonzo.