Popovic was recruited to join in the plot to kill Archduke Franz Ferdinand by Danilo Ilic. A friend of his, Vaso Cubrilovic's and Vaso's older brother, Veljko were already part of the plot. Even though Popovic was given a bomb and a gun and stood along the Appel Quay with the others, he did not act. After the murders, he hid his bomb and gun in the basement of a house near his post on the Appel Quay. He was arrested nine days after the murders, based on Ilic's confession. Popovic and the others were tried in October 1914. For his role in the assassination, Popovic was found guilty of treason. Since he was under 20, the death penalty was not available. Instead, he received a 13 year prison sentence. With the collapse of the Austrian government after the war, Popovic was released from prison.
Cvijetko Popovic went on to become the Curator of Ethnography Department of the Sarajevo Museum.