On 30 December 1941, Stojanović arrived in the Grmeč district, which was in the zone of responsibility of the 1st Krajina National Liberation Partisan Detachment. The Italian troops operating in that area portrayed themselves as protectors of the Serb people. Stojanović's task was to counter such propaganda and mobilise the Partisans of the 1st Krajina Detachment to fight against the Italians. He stayed in the area until mid-February 1942, by which time the Partisan leadership of Bosnia-Herzegovina considered he had completed his tasks successfully. At the end of February 1942, Stojanović was appointed chief of staff of the Operational Headquarters for Bosanska Krajina—a unified command of all Partisan forces in the regions of Bosanska Krajina and central Bosnia. The Operational Headquarters' main task was to counter the rising influence of the Serb nationalist Chetniks in those regions. On 5 March 1942, Stojanović was severely wounded in a Chetnik ambush. He was taken to a field hospital in the village of Jošavka. Members of the Jošavka Partisan Company defected to the Chetniks on the night of 31 March, and took Stojanović prisoner. The next night, a group of Chetniks killed him. In April 1942, the 2nd Krajina Detachment was named Mladen Stojanović in his honour, and a few months later he was posthumously awarded the Order of the People's Hero. After the war, his service to the Partisan cause was commemorated by the construction of a memorial in Prijedor, the naming of streets, public buildings and a park after him, in song and in film.