Gantz was born in Kfar Ahim, Israel in 1959. His mother is a Holocaust survivor, originally from Mezőkovácsháza,Hungary. Gantz 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. During his career Gantz has served in a number of roles, including: Commander of the Shaldag Unit in the Israeli Air Force, Commander of the Paratrooper Brigade, Commander of the Reserves Division in the Northern Command, Commander of the Lebanon Liaison Unit, Commander of the Judea and Samaria Division in 2000, before becoming the Commander of the Israeli Northern Command in 2001, and as Israel's military attaché in the United States from 2005 until 2009 before becoming the Deputy Chief of the General Staff.
Gantz has received a number of degrees during his military service. He is a graduate of the IDF Command and Headquarters College and the National Security College. He holds a bachelor's degree in history from Tel Aviv University, a master's degreein political science from the University of Haifa, and an additional Master's Degree in National Resources Management from the National Defense University in the United States.