Zimmermann had a 19-9 record with a 3.25 ERA and 161 strikeouts last season and finished seventh in the National League Cy Young Award balloting. He was one of 10 Nationals who were eligible for arbitration.
"I knew I was going to be here this year and most likely be back next year," Zimmermann said to MLB.com. "I'm happy to get this out of the way and not worry about the arbitration process this year or next year.
The final two years of salary arbitration eligibility are bought out because of the new deal. Zimmermann is scheduled to be a free agent after the 2015 season.