According to ESPN.com's Jordan Raanan, Marshall made his decision public at the NBC4 Health and Fitness Expo at MetLife Stadium: "Two more years, get my Super Bowl, have a little bit more fun, and then I'm going to go change the world in the mental health space."
Marshall signed a two-year, $11 million deal with the G-Men during the offseason, although New York could release him and incur only $1 million in dead cap space following the 2017 campaign, per Spotrac.
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The 33-year-old veteran spent the past two seasons with the New York Jets.
Although he was named to his sixth career Pro Bowl in 2015 with 109 receptions for 1,502 yards and a career-high (and league-leading) 14 touchdowns, he fell off considerably last season.
Marshall had nagging injuries and ended the campaign with 59 grabs for 788 yards and three touchdowns, which marked his worst production since his rookie season in 2006.
The former Denver Broncos, Miami Dolphins, Chicago Bears and Jets star will join a potent Big Blue offense orchestrated by quarterback Eli Manning.
Marshall will play alongside wide receivers Odell Beckham Jr. and Sterling Shepard, as well as tight end Evan Engram, who was selected in the first round of the 2017 NFL draft at No. 23 overall.
Marshall has never appeared in a playoff game during his 11-year career, but the Giants reached the postseason in 2016 and look to have the pieces needed on both sides of the ball to return in 2017.