Shelah was drafted into the IDF in 1977. He volunteered as a paratrooper in the Paratroopers Brigade, and in 1979 became an officer after completing Officer Candidate School. He fought as a platoon leader and as company commander in reserve Paratroopers brigade in the 1982 Lebanon War and ended up losing an eye in Lebanon in 1983. He later published a book about his experiences, "Guf Sheni". He has been a journalist for Maariv and Yediyot Achronot for 25 years along with hosting popular television news and sports programs. As a journalist, Shelah specialized in writing about security issues and on sports.
Prior to the 2013 Knesset elections he joined the new Yesh Atid party, and was placed sixth on its list. He was elected to the Knesset as the party won 19 seats. He was placed sixth on the party's list for the 2015 elections, and was re-elected as the party won 11 seats.
Shelah lives in the Ginaton moshav, and is widowed with two children.