“I have to say, I am afraid that we are on the brink of civil war,” Nadav Argaman told Israeli army radio.
Shin Bet is the internal intelligence service in Israel, which is also responsible for arresting and interrogating Palestinians.
Commenting on the overhaul plan initiated by the Israeli government, led by Prime Minister Benjamin Netanyahu, Argaman said: "Any legislation that does not command broad consensus will lead the state of Israel into chaos. If the law is passed, we will be a different country."
He also called on security and intelligence leaders in Israel to ask Netanyahu to stop these legislations.
Argaman’s remarks came a few days after a group of 800 former Shin Bet agents sent a letter to Netanyahu and Defense Minister Yoav Gallant demanding them to shelve the judicial plan.
Appointed to head Shin Bet in 2016 by Netanyahu, Argaman led the agency for five years.
Israel has been in political turmoil in recent months over the planned judicial reform, which the opposition called a power grab in favor of executive authority.
The Israeli opposition accuses Netanyahu, who is on trial on corruption charges, of using the judicial overhaul to protect himself from the courts.
Netanyahu denies the charges and rejects any link between the judicial changes and his own case.