Rajačić was born in Lučani, a former village near Brinje in Lika (then Habsburg monarchy, today Croatia).

He studied in Zagreb, Karlovci, Szeged and Vienna before dropping out to join the Imperial Austrian Army in 1809 during the War of the Fifth Coalition.

Apart from being a spiritual leader, Rajačić shared political and military leadership of Serbs at the time of war.

Rajačić formed an alliance with the House of Habsburg after being promised autonomy for opposing the 1848 Hungarian Revolution.

[citation needed] Rajačić assisted the educational development of the Serb people in the Austrian Empire.