The Nationals selected Morales' contract from Triple-A Rochester on Tuesday.
Morales earned a promotion to the big leagues by collecting a .286/.363/.519 batting line with 25 home runs and a 43:111 BB:K over 104 contests this season with Rochester. The 24-year-old has split his time between first and third base this season, and he should see fairly regular playing time down the stretch between those two positions and designated hitter.