Petrov was born in Sofia. His father was Jewish. During World War II, Bulgaria was (for a time) pro-Nazi so he used his non-Jewish mother's surname. He graduated in medicine from Sofia University in 1944. He was politically a leftist and socialist. Between 1947 and 1950, to continue his writing career he worked as a press and cultural attache and traveled to Rome, Italy. He also went to the United States, Switzerland and France.