Schwarber, 28, is on the injured list with a right hamstring strain but is expected to be back within a week or so. He had a monster June before getting hurt, hitting 16 home runs contributing to a 1.122 OPS for the month.
The Nationals are getting minor-league right hander Aldo Ramirez in return for Schwarber. Ramirez, 20, had a 2.03 ERA in eight games for Class A Salem and is currently on the 7-day injured list.
Schwarber signed a one-year, $10 million deal with the Nationals after being non-tendered by the Chicago Cubs last season.
He has an $11.5 million mutual option for 2022 which includes a $3 million buyout. Schwarber should see time at designated hitter, as well as the outfield for the Red Sox.