The Orioles selected Tromp's contract from Triple-A Norfolk on Monday.
Tromp will meet the big-league club in Los Angeles for their three-game series against the Angels. The 31-year-old will join his second major league team this season after playing in 12 games for Atlanta, registering 27 plate appearances prior to signing with Baltimore on June 10. The Orioles designated Michael Siani to make room for Tromp on the roster.