The team on Tuesday signed the veteran defensive pass-rusher to a two-year contract extension through 2018.
NFL Network Insider Ian Rapoport reported that Johnson turned down more money elsewhere to accept the team's offer of $9.5 million over two seasons.
"It's great to have Charles back," coach Ron Rivera told the team's official website. "He has spent his entire career with the Panthers, has emerged as a leader for us in the last few years, and is a big part of the reason we've had the success we've had. We look forward to having Charles continue to be part of our team."
A third-round draft pick in 2007, Johnson ranks second in team history with 67.5 sacks. The 30-year-old finished with four takedowns over 13 games last season and ranked behind just Kony Ealy for team snaps from the end position.