Jimmy Spencer, who took over the role when secondary coach David Gibbs was fired in November, will assist Slowik.
Slowik, who was on Charlie Pell's staff at Florida with Shanahan from 1980 to 1982, broke into coaching as a defensive backs coach. He was a finalist for the Broncos' defensive coordinator job when Ray Rhodes was hired for the position in 2001.
Slowik, 50, coached Green Bay's defensive backs from 2000-03. He also was the Packers' assistant head coach from 2002-03, and has 13 years of NFL coaching experience - eight as a defensive coordinator.
Slowik was a top candidate to coach Green Bay's secondary. Coach Mike Sherman fired Kurt Schottenheimer after the season. The coaching position remains open. The Packers also are seeking a wide receivers coach and a defensive line coach.