NATO Secretary-General Jens Stoltenberg, who has been in his post since 2014, has had his term extended until September 2022, NATO said on March 28.
"Allies expressed their support for the secretary general's work to adapt and modernize NATO and ensure it remains fit for the future," NATO said in a statement.
All 29 allied states voted for the extension.
Stoltenberg's term was due to end in September 2020.
With the extension, the former Norwegian prime minister will be the first alliance chief since Germany's Manfred Woerner to serve longer than five years.
Only former Dutch Foreign Minister Joseph Luns, who was NATO head for 13 years from 1971, will have served in the post longer if Stoltenberg sees out his term.
Stoltenberg said he is "honored" by the decision made by the 29 allies.
"Together we will continue to adapt & modernize our Alliance to keep it fit for the future," he said on Twitter.
Stoltenberg will travel to Washington next week, where he will hold talks with U.S. President Donald Trump, address a joint session of the U.S. Congress on NATO's 70th anniversary, and attend a meeting of NATO foreign ministers.