Kuby was born in Cleveland, Ohio, the son of Ruth Miller, a secretary, and Donald Kuby, a salesman. His mother was from a Jewish family and his father, who died in 1990, was a Franciscan monk who converted to Judaism and became a militant Zionist before becoming Christian again. His parents divorced when he was five years old, after which Kuby lived with his mother. At 13, he joined the Jewish Defense League under the influence of his father, who was a follower of Meir David Kahane. As a teenager he emigrated to Israel, but returned to the U.S. after being disillusioned by what he describes as "anti-Arab racism."