The Nationals announced the deal Monday.
For his career, Cameron has hit .249 with 278 homers, 968 RBIs and 297 steals over 17 seasons with eight clubs.
He was an All-Star in 2001 and has won three Gold Gloves.
Cameron was suspended for the first 25 games of the 2008 season after testing positive a second time for a banned stimulant. At the time his suspension was issued, Cameron blamed the positive test on a tainted supplement.