Shelah was born in Kiryat Bialik. He enlisted in the Israel Defense Forces in 1977 as a soldier in the Paratroopers Brigade, and in 1979 became an officer. He served as a platoon leader and as an executive officer in the paratroopers, and took part in various raids against PLO camps in Lebanon. After he was honourably discharged he fought as a platoon leader and as company commander in reserve Paratroopers Brigade in the 1982 Lebanon War and lost an eye in Lebanon in 1983. He later published a book about his experiences, "Guf Sheni" ().