The Panthers released Johnson in February after a 2017 season in which the former Georgia star was suspended for four games in December for violating the league's policy on performance-enhancing drugs. He also went without a sack for the first time since his rookie year in 2007.
Johnson took full blame for the suspension, saying he took the drug while recovering from back surgery that basically signaled the end of his career.
Prior to that, Johnson was a perennial team captain and quiet leader in the locker room.
"Great team player, good person and leader,'' coach Ron Rivera said.
In an interview with the team website about finalizing his decision to retire, Johnson recalled a conversation with former University of Georgia administrator Carla Johnson while he played for the Bulldogs.
"When I was at Georgia, she asked me, 'What if you don't make it to the NFL?' '' Johnson recalled. "And I forgot that I had told her I was going to be a janitor back in my hometown."
Johnson, from Hawkinsville, Georgia, went on to play 11 NFL seasons for the Panthers after being selected in the third round of the 2007 draft.
In 2012, he signed a six-year, $72 million deal that earned him the nickname "Big Money.'' He had a career-high 12 1/2 sacks that season en route to becoming the first player in team history with four consecutive seasons with at least nine sacks.
Johnson told the team website he wanted to be remembered as "loyal, hard-working.''
"A Panther all the way through,'' he said. "The Panthers were all I knew, and all I ever wanted to know.''