The right-hander gets a raise from the $4.15 million he earned last season after going through arbitration. He went 3-3 with 37 saves and a 3.36 ERA for the Nationals in 2007.
In three full seasons as Washington's top reliever, Cordero has converted more than 80 percent of his save chances, and his 128 saves put him second on the Expos-Nationals career list behind Jeff Reardon's 152.
He set a club record and led the major leagues with 47 saves in 2005 and then went 7-4 with 29 saves and a 3.19 ERA in 2006, when he made $525,000.
Last season, at age 25, Cordero became the second-youngest closer in major-league history to earn his 100th save.
He is 20-14 with a 2.79 ERA in 299 career appearances. He is eligible for free agency after the 2009 season.
With Cordero and his main setup man, Rauch, at the back of the bullpen, the relief corps was one of the strengths for the Nationals last season. The team went 73-89 for fourth place in the NL East in 2007, ending a string of three consecutive last-place finishes.
The Nationals also agreed to terms Friday on one-year contracts with eight other players, including outfielder Lastings Milledge, acquired in the trade that sent catcher Brian Schneider and outfielder Ryan Church to the New York Mets. Milledge received a split contract that would pay him $402,500 if he's in the majors and $145,075 in the minors.
Others agreeing to 2008 deals: left-handers Ross Detwiler, the team's top pick in June's amateur draft, and John Lannan, who made his big-league debut last season; right-handers Garrett Mock and Chris Schroder; infielder Kory Casto; and first basemen Josh Whitesell and Matt Whitney.