Knight, 32, led Jacksonville with 132 tackles last season, his only year with the Jaguars. He also intercepted four passes to increase his career total to 42 -- third-most among active players.
"We're excited to have a veteran of Sammy's caliber joining our secondary," Giants General Manager Jerry Reese said. "We were attracted to how smart he plays and how productive and physical he plays."
Knight has played in 11 NFL seasons with New Orleans, Miami, Kansas City and Jacksonville.
In 174 regular season games -- 168 of them starts -- he has 1,199 tackles, nine sacks, 14 forced fumbles and 12 fumble recoveries. He has intercepted at least four passes in seven seasons, and was named to the Pro Bowl in 2001.