He was a liaison officer in touch with Chetnik Voivode Vojislav Tankosić in Macedonia with the task of transferring arms and men across the border to Turkish-occupied territory.
[7] In the Salonika trial of Black Hand participants in the May Coup, Simić was sentenced to 18 years in prison in absentia, which is why he remained in Russia and after the October Revolution where he became a Colonel in the Red Army.
Simić was in touch with General Dušan Simović, with whom he met on 26 March, the day before the Yugoslav coup d'état took place, and informed him about the Soviet Union's mood to conclude an agreement with Yugoslavia.
As a minister without portfolio, he and Dušan Simović participated in negotiations with Stalin, and immediately after the military coup d'état on 27 March 1941, Mustafa Golubić, the senior NKVD officer and Božin Simić travelled together from Belgrade to Moscow to attend the signing of the Yugoslav-Soviet Union Friendship Agreement.
Because of this stance in 1946, on his way to Ankara to take over the position of Tito's first ambassador there, an attempted assassination was made by a Bulgarian agent, but he survived.