The Nationals announced the deal via their Twitter account Saturday.
Fister was acquired from the Detroit Tigers in a trade this offseason after he went 14-9 with a 3.67 ERA over 208 2-3 innings in 2013.
He made $4,075,000 last season and when submitting his arbitration figure asked that his salary more than double to $8.5 million. The Nationals had offered $5.75 million.
Only one other Nationals player still could go to arbitration, right-handed reliever Tyler Clippard. He asked for a raise to $6.35 million from $4 million; the team offered $4.45 million. Clippard was 6-3 with a 2.41 ERA and 73 strikeouts in 71 innings in 2013.