Hajjarian was born in Javadiyeh neighborhood of Tehran, Iran in 1954 to parents from Kashan. He studied mechanical engineering at Tehran University. In 1977 Hajjarian was enrolled for military service in Gendarmerie. A young Iranian revolutionary during the 1979 Iranian Revolution, he entered the Islamic Revolution Committees before becoming an Intelligence officer in Navy. Hajjarian contneud his education and obtained a PhD in political science from Tehran University. His thesis advisor was Hossein Bashiriyeh. He was one of the students who took over the US embassy in Tehran in 1979.