Cintron, 32, last appeared in the Major Leagues with Washington in 2009. The utility infielder spent last season in the Mets organization, playing in 20 games with Triple-A Buffalo.
The Nationals plan to give rookie Danny Espinosa a shot at the second-base job this season, but he is inexperienced and coming off hand surgery, so Cintron was presumably added for the sake of organizational depth in the event Espinosa is not ready to go by Opening Day.
Cintron broke into the big leagues with the Diamondbacks in 2001 and remained with Arizona through 2005. He's bounced around since then, spending time in a handful of organizations.