The teams announced the trade Tuesday night. The Pirates got left-hander Stephen Tarpley.
The 26-year-old Snider hit .264 with 13 home runs and a career-best 38 RBIs in 140 games for the Pirates last season. He was a first-round draft pick by Toronto in 2006.
The 21-year-old Tarpley was 3-5 with a 3.68 ERA with Class A Aberdeen.
The Orioles also designated catcher Michael Ohlman for assignment.