Jordan Raanan of ESPN noted the release saves the Giants $5.2 million in cap space.
The 34-year-old UCF product finished the 2017 season on injured reserve after suffering an ankle injury in October that required surgery.
Marshall told Ralph Vacchiano of SNY in December he was close to getting full clearance and planned to play for at least a couple more seasons.
"I think I'm two great years away from … and I'll say it: I want to be a Hall of Famer," he said. "And I think I got two great years to go to be mentioned with some of the greats. I'm not playing this game just to be a guy. I want to be remembered for the product that I put on the field."
Marshall failed to make much of an impact during his only year with the Giants. He caught 18 passes for 154 yards with no touchdowns in five appearances.
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His departure will likely make the Dez Bryant speculation grow louder.
"The Giants got a helluva defense, they're going to pay OBJ (fellow wideout and pal Odell Beckham Jr.), so coming back. Playing with him, Sterling (Shepard) ... the tight end (Evan Engram), (QB Eli) Manning? Crazy," Bryant said "... They draft (Penn State running back Saquon Barkley with the No. 2 overall pick)? That'd be crazy!"
Meanwhile, Marshall shouldn't have much trouble latching on elsewhere as a No. 2 or 3 receiver as long as his medical check comes back clean after the failed Giants physical.