He is best known for being the final commander of Croatian legionnaires in World War II, serving in the German Wehrmacht on the Eastern Front in the Battle of Stalingrad, and later joining Yugoslav People's Army.

He received eight years of schooling in Pécs, Hungary; Karlovac, Croatia; and Maribor, Slovenia, before graduating as an artillery/gunnery officer at the Royal Yugoslav Military Academy in Belgrade.

With Mesić as the artillery section commander, the 369th Regiment saw action against Russian forces in October 1941 after an exhausting 35-day, 750 kilometres (470 mi) march to the village of Budinskaja.

Due to illness, regiment commander Colonel Ivan Markulj was transferred back to Croatia and Mesić temporarily replaced him on 7 July 1942.

The regiment attacked Proljet Kultura on 27 July 1942, but an overwhelming Soviet counterattack the next day killed 53 and wounded 186 Legion soldiers.

Its duties consisting of mainly holding the famous Red October factory frontline, where the regiment suffered heavy casualties.

After the surrender of the German Sixth Army by General Paulus on 2 February, Mesić became a prisoner of war, along with fifteen other officers, approximately 100 wounded combat soldiers, and 600 other members of the Croatian Legion.

In an official report dated 30 June 1943, Lieutenant Rudolf Baričević commended Mesić's bravery and leadership, calling him "an exemplary officer" and "true soldier."

Mesić and the remaining members of the legion were first assembled at Beketovka on the Volga River, where they were joined by some 80,000 POWs, consisting mainly of Germans, as well as some Italians, Romanians, and Hungarians.

The brigade subsequently suffered heavy casualties battling retreating German forces during 1945 on the Syrmian Front and near Slavonski Brod.

[2][dead link‍] His Nazi collaboration was forgotten or forgiven, and he lived freely until the Informbiro period, when he was suspected, along with thousands of others, of espionage for Russian secret services.

Mesić lost both of his legs under a running train sometime during 1950 in suspicious circumstances, possibly in UDBA custody when he was being transferred to Belgrade for interrogation.