Thurmond becomes the 10th former Oregon Ducks player brought into the Eagles' fold by coach Chip Kelly, who was Oregon's head coach from 2009 to 2012. Thurmond will pair up with free-agent cornerback Byron Maxwell, who signed a six-year contract worth as much as $63 million (with $25 million guaranteed) to leave the Seahawks.
Thurmond and Maxwell were teammates in Seattle before Thurmond signed a one-year contract with the Giants last offseason.
The Eagles also officially announced that quarterback Mark Sanchez had re-signed with the team on a two-year deal. On Tuesday, the Eagles traded for quarterback Sam Bradford in a deal with the Rams that sent quarterback Nick Foles to St. Louis.
Thurmond was a key part of the Seahawks' 2013 team that won Super Bowl XLVIII. Last offseason, he said he had multiyear offers from several teams, including the Giants, but wanted to take a one-year deal in order to prove himself away from Seattle and try to cash in this offseason.
Unfortunately for Thurmond, those plans were derailed when he tore a pectoral muscle in Week 2 and missed the final 14 games of the season. The Giants had signed him to be their nickel cornerback and believed he also could contribute on the outside if one of their starting outside corners -- Dominique Rodgers-Cromartie or Prince Amukamara -- were to miss time due to injury.
Thurmond, who turns 28 in August, was a fourth-round pick of the Seahawks in 2010. He played the first four seasons of his career in Seattle.
ESPN.com Giants reporter Dan Graziano contributed to this report.