Moss was a prospect for the Red Sox organization, where he made his MLB debut in 2007. During the 2008 season, he was sent to the Pirates as part of a trade to acquire Jason Bay. Moss struggled in Pittsburgh, and he played for the Phillies in 2011. Moss joined the Athletics in 2012, where he became a strong contributor. He was named to appear in the 2014 MLB All-Star Game. After the 2014 season, the Athletics traded him to the Indians. Moss was then traded to the St. Louis Cardinals in 2015.