Frandsen, 32, hit .259 in 105 games with Washington this season while appearing at first base, second base, third base and left field. He has a .259 career batting average and a .662 OPS over parts of eight seasons with San Francisco, the Los Angeles Angels, Philadelphia and Washington.
Frandsen, who has five full years of major league service time, avoided salary arbitration with his new deal.
Frandsen has the same performance bonuses in Friday's deal that were in his 2014 contract: $50,000 each for 225, 300, 350 and 400 plate appearances and $100,000 for 450. He had 236 this year.
Ten Nationals remain eligible for arbitration: pitchers Stephen Strasburg, Doug Fister, Tyler Clippard, Drew Storen, Craig Stammen, Jerry Blevins and Ross Detwiler; infielder Danny Espinosa; and catchers Wilson Ramos and Jose Lobaton.
The Associated Press contributed to this report.