Riddick, 28, had visited the New Orleans Saints and Broncos after he was released.
He has been a valuable pass-catcher in his career with 285 receptions, including a career-high 80 in 2015. He also has 2,238 receiving yards and 14 touchdown receptions in his six NFL seasons. He also has rushed for 1,023 yards with five rushing scores.
But rookie Kerryon Johnson boosted the Lions' running game last year, and Detroit also added veteran running back C.J. Anderson and drafted running back Ty Johnson in the sixth round out of Maryland. The Lions also have a new offensive coordinator in Darrell Bevell.
The Associated Press contributed to this report.