Mr Stoltenberg had been due to step down after eight years in charge of Nato and become the governor of Norway’s central bank. He announced on Thursday that an extension would see him step down at the end of September 2023.
Mr Stoltenberg, who was leading an emergency Nato summit in Brussels on Thursday, confirmed the third extension to his tenure after initially taking up a four-year post in 2014.
There is no formal selection procedure for the secretary general’s job, with a winner emerging from closed-door consultations between diplomats. Any extension would be agreed by consensus.
The civilian role is traditionally held by a European statesman, with a US general taking Nato’s top military post. Mr Stoltenberg is a former prime minister of Norway.
No clear front-runner had emerged in the race to succeed Mr Stoltenberg, although there was speculation that a candidate from Eastern Europe might be chosen to send a message to Moscow.
Russia's invasion has prompted Mr Stoltenberg to order a rethink of Nato's military posture in the East to deal with a more hostile Russia. It comes as the alliance updates a strategic blueprint that was last revised in 2010.