Tulloch, 27, played his first five season with the Tennessee Titans before signing with the Lions prior to last season. He recorded 111 tackles, three sacks and two interceptions while starting all 16 games for the Lions.
Detroit was able to open up some cap space to make the signing by restructuring the contracts of Matthew Stafford, Ndamukong Suh and Nate Burleson. The Lions recently signed wide receiver Calvin Johnson to an eight-year deal worth $132 million, making him the highest paid wide receiver in the NFL.
The Philadelphia Eagles and the Tampa Bay Bucs were also reportedly interested in Tulloch's services.