Martinez gives the Giants the middle linebacker they desperately need. The 2016 fourth-round pick has been a tackling machine with Green Bay, ranking first (155), second (144) and second (144) in the NFL over the past three years.
Martinez, 26, played the second part of the 2019 season with a broken bone in his hand.
He ended up with three sacks, five tackles for loss, a forced fumble and an interception in 2019, but the Packers gave every indication that they were looking to move on.
Overall, in four seasons, he has 512 tackles (332 solo), 10 sacks, 2 forced fumbles, 2 recoveries and 3 interceptions.
The Giants are also expected to sign former 49ers' tight end Levine Toilolo, sources told ESPN's Adam Schefter. Toilolo had two catches for 10 yards in his one season in San Francisco after playing for the Falcons and Lions. New York needed a replacement for the recently retired tight end Rhett Ellison.
ESPN's Rob Demovsky contributed to this report.