Vartanian was born Goar Levonovna Pahlevanyan (), in Gyumri, in what was then the Transcaucasian Socialist Federative Soviet Republic in the Soviet Union and is now Armenia. After her family moved to Tehran, Iran in the early 1930s, she changed her surname to Kandaryan (), where she met her future husband Gevork. She became a member of an anti-fascist group in 1942. They uncovered and prevented Operation Long Jump, an attempt by the Nazis to murder Joseph Stalin, Winston Churchill, and Franklin Roosevelt at the Tehran Conference in 1943.