Howard, 30, is expected to compete with James Hurst at the starting right tackle spot. Baltimore hadn't signed an experienced lineman since losing Rick Wagner, a three-year starter who signed with the Detroit Lions in free agency.
The addition of Howard provides much-needed experience to a thinning offensive line. Pro Bowl guard Marshal Yanda had been the only lineman who started more than 13 games in the NFL. Baltimore lost two linemen -- John Urschel (retirement) and Nico Siragusa (knee) -- for the season since training camp began eight days ago.
Howard, a 6-foot-7, 330-pound lineman, started 39 games over the past three seasons with the Raiders. He was released on July 28 after completing the second season of a five-year, $30 million deal.
The Ravens are familiar with Howard, who spent time on Baltimore's practice squad in 2011.