Diggs has started 80 games during his six-year NFL career, all of those with the Packers.
A fourth-round draft pick out of Ohio State in 2000, Diggs has 541 career tackles, seven sacks and four interceptions. He got a one-year contract from the Panthers believed to be close the league's veteran minimum salary.
In Carolina, Diggs expected to compete for the starting outside linebacker job left vacant by the departure of Will Witherspoon to the St. Louis Rams.
The 6-foot-4, 240-pound Diggs is the second outside linebacker the Panthers have signed in less than a week, joining Keith Adams from the Philadelphia Eagles. Along with Diggs and Adams, second-year player Adam Seward and veteran Chris Draft are also likely to compete for the one opening.
According to general manager Marty Hurney, it's unclear if last year's first-round draft pick Thomas Davis will play weak-side or strong-side linebacker, but it's fairly obvious the Panthers have him pegged to start one of those spots.
Once that decision is made, Diggs and the others will compete at the other outside linebacker spot.
Diggs, 27, has played both outside linebacker spots during his pro career, was limited to nine games last season after tearing the medial collateral ligament in both knees, but had been very durable up until that point starting 62 straight games during one stretch. He's earned the nickname "Nails" for his toughness.