During World War II, he was mobilized in the Croatian Home Guard. In 1942 he tried to escape and join the Yugoslav Partisans. He was captured and imprisoned in Zenica, but was later acquitted of charges of desertion and mobilized again into the armed forces of the Independent State of Croatia. In May 1943, Brnčić escaped for the second time, but before he could join the Partisans he was captured by the Chetniks, who killed him and buried in an unknown location.
