Simmons' coaching career began in 2011 as a defensive assistant with the Green Bay Packers, later having stints with the Carolina Panthers and Las Vegas Raiders.
After one season in that capacity, Simmons was promoted to defensive assistant (secondary), a position he held for 4 years (2012–2015).
He spent 2019 as Green Bay's defensive backs coach, where he helped the team advance to the NFC Championship game and finish the regular season tied for 3rd in the league in interceptions, 3rd in completion percentage allowed, 4th in pass breakups, 5th in forced fumbles, tied for 5th in fewest passing touchdowns allowed and 6th in defensive passer rating.
Cornerback Jaire Alexander added two interceptions and finished tied for fourth in the league in passes defensed with 17.
Darnell Savage was named to the PFWA All-Rookie team after starting all 14 games he appeared and recording 61 tackles, a tackle for loss, a team high two forced fumbles, two interceptions, seven passes defensed, a QB hit and two QB pressures.