Boley had 355 tackles, 3 1/2 sacks and three interceptions in 57 games (including 50 starts) over four seasons with the Giants after signing as a free agent in 2009.
The 30-year-old was a key player in New York's 2011 Super Bowl championship season and appeared in all 16 regular-season games in 2012, racking up 92 tackles and picking off three passes.
"Michael Boley was brought here as a fast, athletic, versatile linebacker," Giants Coach Tom Coughlin said. "We recognized his special skills were in coverage. He's a smart player who made some big plays for us."
Boley amassed 685 tackles, 9 1/2 sacks and eight interceptions in 121 career games (102 starts) with the Giants and the Atlanta Falcons.
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