حركة القوميين العرب
Haddad was born to Palestinian Christian (Greek Orthodox) parents in Safed, Palestine, in 1927. During the 1948 Arab–Israeli War his family's home was destroyed and his family fled to Lebanon. He studied medicine at the American University of Beirut, where he met fellow Palestinian refugee, George Habash, who was also a medical student. Together they helped found the Arab Nationalist Movement (ANM), a pan-Arabist and Arab socialist group aiming to create the State of Palestine and unite the Arab countries.