Martin is in the majors for the first time since signing with the Nationals as a minor league free agent out of the Mexican Winter League in February 2010. He was 3-2 with a 1.39 ERA and 11 saves last year while pitching in three levels of the Nationals' minor league system.
In one appearance this season, he had four strikeouts in two innings and earned the save on April 11 for Syracuse against Scranton/Wilkes-Barre.
Cedeno had a 3.38 ERA and no record in 16 innings over 25 games for Washington starting in 2013.
The Nationals announced the moves before Tuesday night's game at Boston.