Mitchell had been designated for assignment on Monday to make room on the 40-man roster for reliever Todd Coffey, who signed Friday as a free agent.
Mitchell, who turns 27 next week, had brief Major League callups the past two seasons, hitting .151 with four homers in 101 at-bats. He was originally drafted by the Dodgers in 2003.
He underwent arthroscopic surgery on his left wrist for torn cartilage last September.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.