Miller was designated for assignment by Oakland on Dec. 23 after the A's received four players for pitcher Gio Gonzalez.
The 26-year-old Miller went 3 for 12 with a homer and two RBIs for Oakland last season after being called up in September. He played in 110 games with Triple-A Sacramento, batting .276 with 32 home runs and 83 RBIs. Miller also stole 16 bases without being caught.
Miller will compete for a roster spot this spring, Orioles president of baseball operations Dan Duquette said.