He served as Syria's Ambassador to Romania from 1975 to 1980. Next he became the head of authentication and translation department at the foreign ministry in 1980 and his term ended in 1984. Later he served as the head of private offices department from 1984 to 1990. After serving as Syria's ambassador to the United States from 1990 to 2000, Muallem was named as assistant foreign minister in 2000. He was appointed deputy foreign minister in 2005 and given the Lebanese file by president Bashar al-Assad.