The Nationals signed Alfaro to a one-year contract Tuesday, Andrew Golden of The Washington Post reports.
Alfaro recently opted out of his minor-league deal with the Brewers after slashing .244/.285/.430 with 15 home runs and 12 stolen bases with Triple-A Nashville. He'll give the Nationals an experienced catcher with Keibert Ruiz (concussion) still working his way back and Drew Millas (finger) out for the season.