The Packers made the signing official on Tuesday.
Guion's one-year deal is worth $2.75 million, a league source told ESPN's Adam Caplan.
Details of the contract were finalized on Monday morning, and Guion is expected to be signed by Tuesday. The deal comes three days after the free-agent defensive tackle visited the Seattle Seahawks and less than a week after his plea agreement following his February arrest on felony marijuana and firearm possession charges.
Guion, 27, still could face disciplinary action from the NFL, but the charges were dismissed after he paid a $5,000 fine.
Guion started every game for the Packers last season and posted career highs in tackles (62) and sacks (3.5). He played under a one-year, $1 million contract signed in March 2014 following his release from the Minnesota Vikings.
Packers coach Mike McCarthy has maintained throughout the offseason that he would like to have Guion back.
"I think to a man, everybody would like to see Letroy be a Green Bay Packer," McCarthy said last week at the NFL annual meetings in Phoenix.
Guion is the fourth free agent the Packers have re-signed this month, but the first on the defensive side of the ball. They previously re-signed receiver Randall Cobb, tackle Bryan Bulaga and quarterback Scott Tolzien. They have lost a pair of cornerbacks: Tramon Williams to the Cleveland Browns and Davon House to the Jacksonville Jaguars.
NFL Network reported Raji's deal will pay him $3.5 million, and that the deal could reach $4 million with incentives. Last year, Raji returned to the Packers on a one-year, $4 million contract.