Thompson is expected to join the major-league roster Saturday, Jesse Dougherty of The Washington Post reports.
Thompson made his major-league debut earlier this season and allowed a run in three innings across four relief appearances. He's posted a 5.34 ERA and 1.17 WHIP in 28.2 innings at Triple-A El Paso this year, and he'll now get a chance to carve out a big-league role with his new club.