Johnson's contract, which he can't sign until Friday, comes with $32 million guaranteed, the source said. Johnson opted to re-sign with the Panthers after the NFC South rival Atlanta Falcons hotly pursued him.
"The Panthers told me the whole time they were going to come after me hard," Johnson said Tuesday after the team announced it had come to undisclosed financial terms with the player. "I had to see it to believe, but they did."
"Could you have turned that down?" Johnson said with a laugh.
The Panthers put the full court press on Johnson. General manager Marty Hurney, coach Ron Rivera and several members of the defensive staff flew to Miami on Monday night in an effort to make sure Johnson wouldn't get away.
"A lot of people in my family were rooting for me to sign with Atlanta because it was closer to home and they could come see me play," said Johnson, a native of Hawkinsville, Ga. "But I think they understand."
Johnson had a breakout season for the Panthers in 2010, with 11.5 sacks in his first year as a starter. He had a combined 10 sacks in his previous two seasons playing behind Peppers and Tyler Brayton.
Johnson said he was impressed at how important the Panthers made him feel by bringing a good portion of the coaching staff on the trip.
"They showed so much respect for me; I wanted to show it back," Johnson said.
Aside from the money, Johnson said his love of the Charlotte community played a role in his decision.
"Once you are settled in somewhere you get comfortable," Johnson said. "Money aside, it wasn't a hard decision for me to leave because I am tied into Charlotte."
NFL Network insider Jason La Canfora and The Associated Press contributed to this report.