The team did not disclose the length of the contract or financial terms.
Kampman played his first eight NFL seasons with the Green Bay Packers. He has 54 career sacks and recorded at least 9½ sacks per season over three of the past four seasons.
A Pro Bowl selection in 2006 and 2007, Kampman moved to outside linebacker in 2009 as Green Bay shifted to a 3-4 defense. He had 55 tackles, including 3½ sacks, before a knee injury ended his season on Nov. 22.
Kampman flew into Jacksonville on Friday night, met with the team's staff on Saturday afternoon and negotiated into late Saturday night, according to the Florida Times-Union.
He should boost a pass rush that ranked last in the NFL with a franchise-low 14 sacks. The sack total is the fifth-lowest in NFL history.
The Jaguars used veterans, rookies, former first-round draft picks and a few undrafted guys in hopes of generating consistent pass rush last season. Even with different schemes, various blitzes and some new faces, nothing really worked.
Owner Wayne Weaver, general manager Gene Smith and coach Jack Del Rio all vowed to revamp the defensive line, knowing the team stood little chance of making the playoffs without more quarterback pressure.
Jacksonville, which also elevated its special teams with the signing of Kassim Osgood this weekend, targeted Kampman before free agency began Friday. The Jaguars hoped to land Kampman or former Tennessee defensive end Kyle Vanden Bosch, who signed a four-year contract worth $26 million with Detroit.
Kampman's deal could be similar. Although he is coming off a torn anterior cruciate ligament in his left knee, Kampman is a year younger than Vanden Bosch, and despite playing in just nine games in 2009, finished with half a sack more than his counterpart.
Kampman has 592 tackles, 13 forced fumbles and four fumble recoveries in 112 career cames. He was a two-time Academic All-America at Iowa.
Information from The Associated Press was used in this report.