"I tendered the government's resignation," Stoltenberg told reporters after a brief cabinet session attended by King Harald V.
He had previously said upon admitting defeat in the September 9 parliamentary polls that he would step down after the drafting of the 2014
budget, which was unveiled on Monday as scheduled.
Conservative leader Erna Solberg, who is forming a minority coalition with the anti-immigration populist Progress Party, is expected to become the next
prime minister on Wednesday.
In a country where minority governments are the norm, the conservatives and populists won 77 of the 169 parliamentary seats, but can also count on support from the 19 MPs from allied centre right parties.
The Progress Party is set to join government for the first time since its creation 40 years ago.
It comes two years after former party member Anders Behring Breivik killed 77 people, including 69 during a rampage at a Labour Youth camp on the island
Stoltenberg, in the job since 2005, had received widespread praise for his economic stewardship and for finding the right words when the grief-stricken
nation tried to deal with the 2011 massacre.
But Stoltenberg had already experienced rare longevity in power by Norwegian standards and the cracks in his administration exposed by the
aftermath of Breivik's killing spree eventually cost him dearly.