Zadro was born in a small village Donji Mamići near Grude in Herzegovina, and his family moved to Borovo Naselje in 1954 where he finished school. He became active in politics during Croatia's first democratic elections in 1990; he founded branch of Croatian Democratic Union (HDZ) for Municipality of Vukovar and became the vice president of the HDZ in Vukovar, and joined the defense corps when the war started.