The Chicago Bears agreed to terms Thursday year contract.
Bush, 27, became Oakland's feature back last season when starter Darren McFadden was lost to a foot injury in a Week 7 loss to Kansas City.
The 6-foot-1, 245-pound Bush set career highs in attempts (256), rushing yards (977), receptions (37) and receiving yards (418).
Drafted by the Raiders in the fourth round of the 2007 NFL Draft out of Louisville, Bush has amassed 2,642 yards and 21 touchdowns on 632 carries in 61 career games. He has also caught 91 passes for 879 yards and one score.