The 36-year-old veteran is expected to travel with the team to Port St. Lucie for Saturday's spring game against the New York Mets. Romero is expected to begin the season with Triple-A Syracuse, but manager Davey Johnson said Friday he provides "insurance" for the Nationals, in case they need another left-handed reliever.
Romero, who recently pitched for Puerto Rico in the World Baseball Classic, has played for eight teams in a 14-year career. He pitched for three different teams in both the 2011 and 2012 seasons.
In 680 career games, he has a 34-28 record with seven saves and a 4.16 ERA.