The Packers historically don't participate in the free-agent market, but specific needs at several positions have pushed them into the fray.
His star-crossed career includes a year-long suspension in 2008 for violating the league's substance-abuse policy, but on the field he always has been considered an aggressive pass-rusher. That skill should fit well with the Packers, whose depleted pass rush last season was a primary reason for their defensive collapse.
"When you think of this team," Hargrove said, "you think of one of the most respected organizations in the league. For them to come after me is very moving. I feel blessed today."
Hargrove has 19½ sacks in 102 career regular-season games. He had three sacks in 15 games for Seattle last season.
The Packers did not immediately announce the signing of Hargrove. But the team did finalize a contract with cornerback and special teams ace Jarrett Bush, who agreed to terms last week.
Hargrove acknowledged his excitement about joining the Packers in a post on his Twitter account, saying, "Here I come Packer Nation."
Information from The Associated Press was used in this report.