The 6-foot-2, 296-pound Johnson will be reunited with Carolina defensive coordinator Ron Meeks, who had the same job in Indianapolis in 2007 when Johnson started all 16 games and recorded 63 tackles as an undrafted rookie.
Johnson's career has declined since. The Colts waived him early in the 2008 season following his arrest on a marijuana possession charge. He was re-signed, then cut again early last season because coach Jim Caldwell said his play had slipped.
The 26-year-old Johnson also ran into trouble at Penn State, where he was temporarily kicked out of school and later suspended from a bowl game.
The Panthers, who have been wary of signing and drafting players with off-field issues in the past several years, decided to take a chance on Johnson.
"We have done a lot of research on Ed," Panthers general manager Marty Hurney said in a statement. "When we took into account what people around him said and the impression we got when meeting with him in person, we felt comfortable giving him this opportunity."
Johnson will provide insurance for Maake Kemoeatu, who is recovering from a ruptured Achilles tendon that forced him to miss all of last season. Carolina had trouble replacing him before 36-year-old Hollis Thomas filled in capably to close the season.
What the rest of the defensive line will look like in 2010 is also uncertain.
The Panthers have still not announced if they'll place the franchise tag on five-time Pro Bowl defensive end Julius Peppers by the Feb. 25 deadline and offer him a guaranteed $20.1 million for one season.
The other starting defensive end from 2009, Tyler Brayton, will be an unrestricted free agent.