Former Shin Bet chief Yoram Cohen announced his joining Gadi Eisenkot's Yeshar party.
Cohen and Eisenkot served concurrently as Chief of Staff and head of the Shin Bet during Cohen's last year in office.
Cohen, who joined the "Not Bibi" camp, was considered to have right-wing views and was courted by several elements in the political system.
Eisenkot said: "Yoram - welcome. We will return Israel to a straight and ethical path, with security strength and a unifying and hopeful leadership that will connect the people of Israel.".