Forester was selected in the third round (31st overall) of the 1953 NFL draft by the Green Bay Packers. He played on the Packer defense for 11 seasons, from 1953 through 1963, as a defensive tackle for three of his first four seasons, with one season at left outside linebacker. He then moved to middle linebacker for a few games in 1957, and later to the right side where he would play the rest of his career at. Forester played under four head coaches in Green Bay; the last was Vince Lombardi, who arrived in his seventh season in 1959. He was a member of Lombardi's first two NFL championship teams in 1961 and 1962, both wins over the New York Giants.