Richardson, the No. 3 overall pick of the 2012 draft, was out of football last season. Terms of the deal were not immediately announced.
The sides first talked in February, but the Ravens wanted Richardson to be in better condition before signing him. He reached a deal on Monday morning, just before the start of the Ravens' offseason workout program.
Richardson, who will turn 26 in July, needs a strong offseason and training camp to find a spot in Baltimore's crowded backfield. The Ravens currently have Justin Forsett, Buck Allen, Lorenzo Taliaferro, Terrance West and Terrence Magee at running back.
One of the bigger busts of the 2012 draft, Richardson has played for the Cleveland Browns, Indianapolis Colts and Oakland Raiders. He has struggled with injuries and his weight over his three-year career, averaging 3.3 yards per carry.