The Washington Nationals have agreed to year contract.
The deal is contingent upon Jackson passing a physical.
Jackson, 28, entered the majors in 2003 with the Dodgers. Over nine seasons the journeyman righty has compiled a 60-60 record with a 4.46 earned right average in 203 appearances (173 starts) for Los Angeles, Tampa Bay, Detroit, Arizona, the Chicago White Sox and St. Louis.
Despite a middling start in 2011 with the White Sox, going 7-7 with a 3.92 ERA in 19 starts, Jackson was traded to the Cardinals on July 27. His luck turned around there, however, as he posted a 5-2 record with a 3.58 ERA during his time with St. Louis.
During the Cardinals' run to a World Series championship last season, Jackson went 1-1 with a 5.60 ERA in four postseason starts.
Jackson also pitched in the postseason with Tampa Bay in 2008, was an All-Star in 2009 with the Tigers and threw a no-hitter with Arizona in 2010.