He collaborated, from 1941 until 1942, with the collaborationist government of Milan Nedić as an officer in the Serbian State Guard and the county prefect of Požarevac.

In 1912, with the start of the First Balkan War, Milan fled to the Kingdom of Serbia and joined the Serbian Army as a volunteer.

[1] In February 1924, Kalabić and five other members of the gendarmerie arrested Montenegrin officers and brothers Stevan and Šćepan Mijušković [sr] along with some relatives and friends for no apparent reason.

[2] Kalabić became an officer of the Serbian State Guard (SDS) following the Axis invasion and occupation of the Kingdom of Yugoslavia.

He was also appointed prefect for the county of Požarevac and passed on information and military supplies to the Chetniks, with whom his son, Nikola, fought and served as a commander.