Neuvirth, 22, was scheduled to become a restricted free agent at the end of this season.
Neuvirth, who led the Capitals' AHL Hershey team to two straight Calder Cup titles, is challenging Semyon Varlamov for the starting goaltender job.
Neuvirth was 9-4 last season with a 2.75 goals-against average and no shutouts, getting playing time when Varlamov and Jose Theodore were injured.
Varlamov was 15-4 with a 2.55 GAA and two shutouts in 23 starts.
"We're really high on him. We're high on both of our goaltenders," Capitals general manager George McPhee said Tuesday. "We've been waiting for this time because we think we drafted two outstanding goaltenders and they're ready to play."
Information from ESPN.com's Scott Burnside was used in this report.