The two-year deal is valued at $12.2 million and includes a fully guaranteed first year of $5 million, with an injury guarantee in the second, sources said.
Cook, 29, was a key component to the Packers' midseason turnaround last season from 4-6 to the NFC title game, which prompted quarterback Aaron Rodgers to say Cook "needs to be near the top of the priority list [to re-sign], the way he played this year."
Cook signed a one-year, $2.75 million contract with the Packers last March after he was released following three seasons with the Rams. He spent the first four years of his career with the Titans.
Martellus Bennett's recent addition to the Packers signaled Cook wouldn't return to Green Bay.
Last season was Cook's first on a playoff team, and he called it "the most fun" he's had in his eight-year NFL career, during which he's caught 303 passes for 3,880 yards and 17 touchdowns.
Although he missed six games because of an ankle injury, he averaged 12.6 yards per catch and had 3 touchdowns in 13 games, including the playoffs. His biggest play of the season was the sideline catch with three seconds remaining to set up the game-winning field goal against the Cowboys in the NFC divisional playoff game.
Information from ESPN's Adam Caplan and Josina Anderson and Rob Demovsky was used in this report.