17 years old in 1914 and a high school student, Cubrilovic was recruited to join in the plot to kill Archduke Franz Ferdinand by Danilo Ilic. Vaso Cubrilovic's older brother, Veljko, was already an accomplice to the plot by providing assistance to the three Black Hand trained assassins. Even though Vaso was given a bomb and stood along the Appel Quay with the others, he did not act. He was arrested about a week after the murders, based on Ilic's confession. Vaso, his brother Veljko, Danilo Ilic and the others were tried in October 1914. For his role in the assassination, Vaso was found guilty of treason. Since he was under 20, the death penalty was not available. Instead, he received a 16 year prison sentence. With the collapse of the Austrian government after the war, Vaso was released from prison.
Vaso Cubrilovic went on to become a teacher, then a university professor. Later, he served as Minister of Forests in the Tito government.