From May 1938 until 1940, he served as chief of general staff, in which position he replaced General Milutin Nedić. He joined other officers in a coup against the government of Dragiša Cvetković. After the coup, Simović became the new prime minister. He did not have much time to prepare for the coming war. On the wedding day of his daughter, Nazi Germany invaded Yugoslavia on 6 April 1941.