القوات اللبنانية
He started his military service in 1969 following incidents which he fought against the Palestinian Liberation Organization (PLO) in Lebanon. He was one of the founding members of the BG Unit and fought against the PLO again in 1975. In 1978, he was appointed into the military intelligence. On September 13, 1982, one day before Lebanese Forces leader and former Lebanese President Bashir Gemayel was killed, Fadi was appointed leader of the Lebanese Forces. He stayed leader of the Lebanese Forces until the election of Fouad Abou Nader.