A pinch-hitting specialist who came up as a second baseman but has also played at first and in the outfield, Anderson hit .264 with seven homers and 19 RBI in 235 at-bats with the New York Mets last season.
He batted .321 (18-for-56) with a homer and six RBI off the bench in 2005, ranking second among NL pinch-hitters in hits and fourth in average.
"Marlon Anderson has been one of the best left-handed pinch-hitters in baseball the last three years," general manager Jim Bowden said. "One of our goals this offseason was to improve our bench, especially from the left side of the plate. Marlon's signing addresses this issue and adds a veteran presence in our clubhouse."
In eight seasons with four clubs, Anderson has a .264 average with 47 homers and 296 RBI. But he's a career .308 pinch-hitter, and his 35 hits off the bench the last two seasons are the most in the majors.
Anderson, who turns 32 in January, is the third player to agree to a contract among the 182 who filed for free agency, following left-hander Scott Eyre with the Chicago Cubs and third baseman Geoff Blum with San Diego.
Anderson's deal with the Nationals pays $925,000 per season. He made $750,000 this year but the Mets didn't want to offer a two-year contract.
"He did a good job," Mets general manager Omar Minaya said. "We felt for that kind of role, we'd like to stick with one year."