Shai Nitzan interned in 1985 with the judge and later President of the Supreme Court, Aharon Barak, and later with the late Attorney Jacob Rubin, then head of the Bar Association. After his internship, Nitzan joined the State Attorney's Office and has been working there ever since. Nitzan has served in the State Prosecutor's Office, including assistant to State Attorney Dorit Beinisch, an attorney in the High Court of Justice Department, and a security affairs officer in the State Prosecutor's Office. Over the years, Nitzan has represented the state authorities in numerous petitions in the Supreme Court in criminal, security and administrative matters, and has been instrumental in making decisive decisions and formulating the State Attorney's policy in many areas.

Nitzan is married and has five children. He was born in Jerusalem, was educated in the Bnei Akiva yeshiva "Nativ Meir" and served as a fighter in the 890th Battalion of the Paratroopers Brigade. He holds a bachelor's and master's degree in law (cum laude) from the Hebrew University of Jerusalem, a BA in Jewish history from the Hebrew University and a master's degree in political science from the University of Haifa and a graduate of the National Security College.