Richardson has given a two-year, $3.4m deal by Oakland, who desperately needed a running back after the retirement of Maurice Jones-Drew.
The 24-year-old was cut by the Indianapolis Colts after a poor 2014, when he managed only 515 yards and three touchdowns and did not play in either of their two play-off games.
Richardson will compete with Latavius Murray for the starting gig with the Raiders.
He was picked third overall in the 2012 NFL Draft by the Cleveland Browns but has proved ineffective despite a sparkling college career at Alabama.
Richardson has never had a 1,000 yard season in his four-year career, and his best season was as a rookie when he had 950 yards and 11 touchdowns.. He only managed two games in the 2013 season for Cleveland before being traded to Indy in 2013 in exchange for the Colts’ 2014 first round pick.
But he remains confident in his ability to be an NFL starter, as he said:??”If a guy is coming in and doesn’t expect to be a starter, why is that guy here? For me, I expect to be a starter wherever I’m at. I just can’t wait for the opportunity.
“Hopefully this is my last stop, and I’m going to do whatever I can to make this my last stop. Until I’m ready to walk away from the game, I don’t want to leave here.”