Cabrera, 27, was 8-10 with a 5.25 ERA for the Orioles this past season. Known for his fastball, curveball and changeup, Cabrera will join a rotation that will include left-handers Scott Olsen and John Lannan.
According to one source, the Nationals beat out the Mets and Pirates for Cabrera's services.
Nationals general manager Jim Bowden was not available for comment and Mike Gazda, the director of media relations for Washington, said the team has nothing to announce at this time.
Cabrera spent the last five years with Orioles and compiled a 48-59 record with a 5.05 ERA for Baltimore.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.