Webb had a 2.91 ERA with the Miami Marlins in 2013 and reached career highs with 66 games, 80 1/3 innings and 54 strikeouts. He was 2-6. Webb, 27, originally was selected in the fourth round of the 2004 amateur draft by Oakland.
In five major league seasons, Webb has a 3.29 ERA in 266 games with San Diego and Miami. He has a 13-15 record and is 0-for-9 in save opportunities, including 0-for-3 last season.
He was one of 17 NL players to have at least 60 appearances and pitch at least 60 innings in both 2012 and 2013.
The signing, announced Tuesday, gives the Orioles 38 players on the 40-man roster.