Father Đujić left Strmica as a priest shortly prior to the Nazi German attack on Yugoslavia on April 6 1941, when he arrived back from Belgrade after participating in the demonstrations against the concordat with the Catholic Church and Yugoslavia.
With the arrival of the Italian military in the Knin region, he was able to establish a military camp within the Italian zone to organize attack on Croat civilians, under the excuse of protection of Serb civilians.
In the summer of 1941, Momčilo became head of the Chetnik detachment in Dalmatia. In September (1941), he became commander of the "Petar Mrkonjić" regiment. In 1942, he became involved in the establishment of the Dinara Chetnik Division. In the name of the Division's HQ, he called on the Serb population for a military uprising against the Ustaša government on February 15, 1942..
The Dinara Chetnik Division had been involved in military actions against the Tito's partisans and Ustaše. He actively cooperated with Italian fascist forces, that gave him refuge and military and political protection, when NDH authorities, as well as military and police forces went to intervene against him. Also, he's also known for his cooperation with German nazi forces, as it was seen in photos, where Đujić is together with Wehrmacht and SS officers.
But, most of his "military actions" were the actions against civilians, Croats, but also against the Serbs, that didn't want to join or support Chetniks.
Tito's biographer Dedijer in his work "Novi prilozi za biografiju J. B. Tita" (New additions for biography of Josip Broz Tito) wrote that "Dinara Chetnik division, under the command of Momčilo Đujić, brought a daily command on clearing the Lika and Northern Dalmatia from Croats and Muslims.
Đujić and his fellow chetnik combatants have in Oct 1942 surrounded and brutally killed Croat civilians in villages Gata, Tugare, Čisla, Gornji Dolac, Ostrvica, Naklice, Zvečanje etc (Poljica area, in the very eastern neighbourhood of Split). The victims were mostly children, older persons and women. Only in Gata, 160 persons were killed, 70 houses were burned, the rest was plundered.
In December 1944 with the subsequent advancement of the Red Army into Yugoslavia, the circumstances in the country became more difficult. Serbian fascist politician Dimitrije Ljotić petitioned to Nazi party official Hermann Neubacher that Đujić's forces be allowed to pass through Croatian-held territory to the Slovenian lands under German control. Neubacher put pressure on Croatian leader Ante Pavelić, so that beginning on December 3 Đujić led the Dinara Chetnik Division out of Dalmatia and into Slovenia and Italy . In May 1945 near Soča. Đujić and his Chetniks met up with the Allies and were interned in the Ebola dispalaced persons camp in Italy. Later on, he moved to America, and Canada, where he established the Movement of Serbian Chetniks "Ravne Gore".
On June 28, 1989, the day of the 600th anniversary of the Battle of Kosovo, Đujić granted the title of Vojvoda to Vojislav Šešelj , then a leading nationalist dissident and now leader of the Serbian Radical Party (SRS). Later in 1998, Đujić rescinded the title of vojvoda as Šešelj was seen as collaborating with then President of FR Yugoslavia Slobodan Milošević .
In the testimony of rebel Croatian Serb leader Milan Babić, Momčilo Đujić supported financially the rebellion of Croatian Serbs in 1990's., , , .