Valencia was designated for assignment by Boston last week after coming to the organization in an August trade with the Minnesota Twins, who received outfielder Jeremias Pineda at the time.
The 28-year-old Valencia, primarily a third baseman, hit .188 with a .199 on-base percentage and a .299 slugging percentage in 44 Major League games this past season with Boston and Minnesota. He placed third in American League Rookie of the Year Award voting in 2010 and enjoyed his best season in '11, when he hit .246 with 15 home runs and led the Twins with 72 RBIs in 154 games. He also led Major League third basemen that season with 260 assists.
In 326 career plate appearances against left-handed pitchers, Valencia is a .316/.359/.472 hitter, and he posted a .226/.214/.377 line in 56 such plate appearances in the Majors last season.
Mahoney, 25, batted .265/.319/.389 in 132 games for Triple-A Norfolk in 2012. He made his Major League debut on July 7 and appeared in two games for the Orioles, going 0-for-4.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.