Bell, 29, didn’t show much explosiveness in his five games with Baltimore, averaging a career-worst 2.7 yards per carry .
Bell, who was behind Latavius Murray and Devonta Freeman in the backfield pecking order, never started a game for the Ravens and never participated in more than 42% of their snaps in a game.
“I really appreciate everything about him: professionalism, attitude, work ethic,” Harbaugh said.
A second-round pick by the Pittsburgh Steelers in 2013, Bell was one of the top running backs in the league from 2013 to 2017, averaging 128.9 total yards per game.