Free-agent first baseman Adam LaRoche has signed a two-year contract with the Nationals, SI.com has learned.

Washington will be looking to LaRoche to replace Adam Dunn, who signed with the White Sox in December. Like Dunn, LaRoche bats left-handed, and he would join a middle of the lineup that includes new arrival Jayson Werth and third baseman Ryan Zimmerman, who both are right-handed hitters.

LaRoche, who has played for the Braves, Pirates, Red Sox and Diamondbacks, hit .261 with 25 home runs and 100 RBIs last year in Arizona.

LaRoche is the second significant addition of the offseason for the Nationals, who are coming off three consecutive last-place finishes in the NL East. Right fielder Werth signed a seven-year, $126 million contract to come over as a free agent from the Philadelphia Phillies, a deal announced at the outset of baseball's winter meetings last month.

The addition of LaRoche should complete Washington's starting infield, which is expected to include Ian Desmond at shortstop and Danny Espinosa at second base. LaRoche is the older brother of Pirates third baseman Andy LaRoche and son of former major league pitcher Dave LaRoche.

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