General manager Reggie McKenzie announced Tuesday that Barron is the first offensive player added to the team this offseason.
Barron was a first-round pick by St. Louis in 2005. He has played 87 games and has experience at both left and right tackle. Oakland previously re-signed right tackle Khalif Barnes, who can play guard as well as tackle. Jared Veldheer is expected to remain the starter at left tackle.
Barron has not played a game since 2010. He sat out the 2011 season with a knee injury and went to training camp with Seattle last summer but did not make the team.